Let's try this again.  Detect older and new versions of ffmpeg and allow for their coexistence within VLC. 

Update references to ffmpeg header files to match new directory structure.  All ffmpeg headers should now be accessed through: 
* <libpostprocess/postprocess.h>
* <libswscale/swscale.h>
* <libavutil/avutil.h>
* <libavcodec/avcodec.h>
* <libavformat/avformat.h>

cmake: Try to compensate for new ffmpeg directory structure by setting HAVE_LIBSWSCALE_TREE if swscale.his found.

cmake: Code clean up, set up options before we start including custom macros, add CONTRIB_INCLDE to CMAKE_REQUIRED_INCLUDES if ENABLE_CONTRIB is set, and correctly discover postproc/postprocess.h header by temporarily adding FFmpeg_CFLAGS to CMAKE_REQUIRED_FLAGS before checking for the header.

cmake: Add qt4 resources. Enable qt4 plugin compilation with cmake's CVS. (known not to work with cmake version 2.4-patch 7
)