Refactored detecting several Apple-related technologies.

Now the HAVE_* macros are set using cvconfig.h. Previously most
of them already were there, but were always undefined. One,
HAVE_COCOA, I had to add.

This also makes the CMake code more consistent; now, WITH_* variables
are always checked in cmake/*, while HAVE_* variables are checked in
modules/highgui/CMakeLists.txt.

cmake/OpenCVFindLibsGrfmt.cmake

@@ -161,4 +161,9 @@ endif()
 #cmake 2.8.2 bug - it fails to determine zlib version
 if(ZLIB_FOUND)
   ocv_parse_header2(ZLIB "${ZLIB_INCLUDE_DIR}/zlib.h" ZLIB_VERSION)
-endif()
+endif()
+
+# --- Apple ImageIO ---
+if(WITH_IMAGEIO)
+  set(HAVE_IMAGEIO YES)
+endif()