Improved error message when boost isn't found.

dlib/add_python_module

@@ -59,57 +59,55 @@ if (PYTHON3)
     FIND_PACKAGE(Boost 1.41.0  COMPONENTS python-py34 )
     if (NOT Boost_FOUND)
         # But if you don't find it then try looking for a module called python.
-        FIND_PACKAGE(Boost 1.41.0 COMPONENTS python REQUIRED)
+        FIND_PACKAGE(Boost 1.41.0 COMPONENTS python)
     endif()
     FIND_PACKAGE(PythonLibs 3.4 REQUIRED)
 else()
-    FIND_PACKAGE(Boost 1.41.0 COMPONENTS python REQUIRED)
+    FIND_PACKAGE(Boost 1.41.0 COMPONENTS python)
     FIND_PACKAGE(PythonLibs 2.6 REQUIRED)
 endif()
+
 if (NOT Boost_FOUND)
+    message(STATUS " *****************************************************************************************************")
     if (WIN32)
-        message(" Set the BOOST_ROOT and BOOST_LIBRARYDIR environment variables before running cmake. ")
-        message(" E.g.  Something like this: ")
-        message("    set BOOST_ROOT=C:\\local\\boost_1_57_0 " )
-        message("    set BOOST_LIBRARYDIR=C:\\local\\boost_1_57_0\\stage\\lib")
-        message("")
-        message(" You will also likely need to compile boost yourself rather than using one of the precompiled ")
-        message(" windows binaries.  Do this by going to the folder tools\\build\\ within boost and running ")
-        message(" bootstrap.bat.  Then run the command: ")
-        message("    b2 install")
-        message(" And then add the output bin folder to your PATH.  Usually this is the C:\\boost-build-engine\\bin")
-        message(" folder. Finally, go to the boost root and run a command like this:")
-        message("    b2 --with-python address-model=64 toolset=msvc --build-type=complete")
-        message(" When it completes, set BOOST_LIBRARYDIR equal to wherever b2 put the compiled libraries.")
-        message(" Note that you will need to set the address-model based on if you want a 32 or 64bit python library.")
-        message("")
-        message(" Next, when you invoke cmake to compile dlib you may have to use cmake's -G option to set the ")
-        message(" 64 vs. 32bit mode of visual studio.  Also, if you want a Python3 library you will need to ")
-        message(" add -DPYTHON3=1.  You do this with a statement like: ")
-        message("    cmake -G \"Visual Studio 12 2013 Win64\" -DPYTHON3=1 ..\\..\\tools\\python")
-        message(" Rather than:")
-        message("    cmake ..\\..\\tools\\python")
-        message(" Which will build a 32bit Python2 module by default on most systems.")
-        message("")
+        message(STATUS "We couldn't find the right version of boost python.  If you installed boost and you are still "
+                "getting this error then you might have installed a version of boost that was compiled with a different "
+                "version of visual studio than the one you are using.  So you have to make sure that the version of "
+                "visual studio is the same version that was used to compile the copy of boost you are using.")
+        message(STATUS " Set the BOOST_ROOT and BOOST_LIBRARYDIR environment variables before running cmake. ")
+        message(STATUS " E.g.  Something like this: ")
+        message(STATUS "    set BOOST_ROOT=C:\\local\\boost_1_57_0 " )
+        message(STATUS "    set BOOST_LIBRARYDIR=C:\\local\\boost_1_57_0\\stage\\lib")
+        message(STATUS "")
+        message(STATUS " You will also likely need to compile boost yourself rather than using one of the precompiled ")
+        message(STATUS " windows binaries.  Do this by going to the folder tools\\build\\ within boost and running ")
+        message(STATUS " bootstrap.bat.  Then run the command: ")
+        message(STATUS "    b2 install")
+        message(STATUS " And then add the output bin folder to your PATH.  Usually this is the C:\\boost-build-engine\\bin")
+        message(STATUS " folder. Finally, go to the boost root and run a command like this:")
+        message(STATUS "    b2 --with-python address-model=64 toolset=msvc --build-type=complete")
+        message(STATUS " When it completes, set BOOST_LIBRARYDIR equal to wherever b2 put the compiled libraries.")
+        message(STATUS " Note that you will need to set the address-model based on if you want a 32 or 64bit python library.")
+        message(STATUS "")
+        message(STATUS " Next, when you invoke cmake to compile dlib you may have to use cmake's -G option to set the ")
+        message(STATUS " 64 vs. 32bit mode of visual studio.  Also, if you want a Python3 library you will need to ")
+        message(STATUS " add -DPYTHON3=1.  You do this with a statement like: ")
+        message(STATUS "    cmake -G \"Visual Studio 12 2013 Win64\" -DPYTHON3=1 ..\\..\\tools\\python")
+        message(STATUS " Rather than:")
+        message(STATUS "    cmake ..\\..\\tools\\python")
+        message(STATUS " Which will build a 32bit Python2 module by default on most systems.")
+        message(STATUS "")
     else()
-        message("")
-        message(" *****************************************************************************************************")
-        message(" To compile Boost.Python yourself download boost from boost.org and then go into the boost root folder")
-        message(" and run these commands: ")
-        message("    ./bootstrap.sh --with-libraries=python") 
-        message("    ./b2")
-        message("    sudo ./b2 install")
-        message(" *****************************************************************************************************")
-        message("")
+        message(STATUS " To compile Boost.Python yourself download boost from boost.org and then go into the boost root folder")
+        message(STATUS " and run these commands: ")
+        message(STATUS "    ./bootstrap.sh --with-libraries=python") 
+        message(STATUS "    ./b2")
+        message(STATUS "    sudo ./b2 install")
     endif()
+    message(STATUS " *****************************************************************************************************")
+    message(FATAL_ERROR " Boost python library not found. ")
 endif()
 
-if (WIN32 AND NOT Boost_LIBRARIES)
-    message(FATAL_ERROR "We couldn't find the right version of boost python.  If you installed boost and you are still "
-            "getting this error then you might have installed a version of boost that was compiled with a different "
-            "version of visual studio than the one you are using.  So you have to make sure that the version of "
-            "visual studio is the same version that was used to compile the copy of boost you are using.")
-endif()
 
 
 INCLUDE_DIRECTORIES("${Boost_INCLUDE_DIRS}")