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.
ca8b621b4f