Added a bunch of unit tests for the various forms of structured svm.

dlib/test/CMakeLists.txt

@@ -101,6 +101,7 @@ set (tests
    svm_c_linear.cpp
    svm.cpp
    svm_multiclass_linear.cpp
+   svm_struct.cpp
    symmetric_matrix_cache.cpp
    thread_pool.cpp
    threads.cpp

dlib/test/makefile

@@ -111,6 +111,7 @@ SRC += string.cpp
 SRC += svm_c_linear.cpp
 SRC += svm.cpp
 SRC += svm_multiclass_linear.cpp
+SRC += svm_struct.cpp
 SRC += symmetric_matrix_cache.cpp
 SRC += thread_pool.cpp
 SRC += threads.cpp