Added Mac specific include directory.

CMake/PolycodeIncludes.cmake

@@ -4,6 +4,7 @@ IF(MSVC)
     INCLUDE_DIRECTORIES(${Polycode_SOURCE_DIR}/Core/Build/MSVC/Polycore)
 ELSEIF(APPLE)
     ADD_DEFINITIONS(-DGL_GLEXT_PROTOTYPES)
+    INCLUDE_DIRECTORIES("${Polycode_SOURCE_DIR}/Core/Build/Mac OS X")
 ELSE(MSVC)
     ADD_DEFINITIONS(-DGL_GLEXT_PROTOTYPES)
     INCLUDE_DIRECTORIES(${Polycode_SOURCE_DIR}/Core/Build/Linux)