Made cmake not use the installed libjpeg on apple systems because it's broken

on some newer OS X installs.

dlib/CMakeLists.txt

@@ -271,10 +271,11 @@ if (NOT TARGET dlib)
          # try to find libjpeg 
          find_package(JPEG QUIET)
          # Make sure there isn't something wrong with the version of libjpeg 
-         # installed on this system.  
+         # installed on this system.  Also don't use the installed libjpeg
+         # if this is an APPLE system because apparently it's broken (as of 2015/01/01).
          set(CMAKE_REQUIRED_LIBRARIES ${JPEG_LIBRARY})
          CHECK_FUNCTION_EXISTS(jpeg_read_header LIBJPEG_IS_GOOD)
-         if (JPEG_FOUND AND LIBJPEG_IS_GOOD)
+         if (JPEG_FOUND AND LIBJPEG_IS_GOOD AND NOT APPLE)
             include_directories(${JPEG_INCLUDE_DIR})
             set (dlib_needed_libraries ${dlib_needed_libraries} ${JPEG_LIBRARY})
          else()