CMake <= 2.8.11 compatibility

Keep compatible with cmake <= 2.8.11 by using the legacy PATH alias for
DIRECTORY with get_filename_component.

Author: speleo3

CMakeLists.txt

@@ -258,7 +258,7 @@ INSTALL (TARGETS ${MSGPACK_INSTALLTARGETS} RUNTIME DESTINATION ${CMAKE_INSTALL_B
                                            LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
                                            ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})
 FOREACH (file ${msgpackc_HEADERS})
-    GET_FILENAME_COMPONENT (dir ${file} DIRECTORY)
+    GET_FILENAME_COMPONENT (dir ${file} PATH)
     INSTALL (FILES ${file} DESTINATION ${CMAKE_INSTALL_PREFIX}/${dir})
 ENDFOREACH ()
 IF (NOT MSVC)