Include the headers for libavfilter, libswscale and libpostproc when
they are enabled (and thus linked in).

Without this change, Sun Studio will fail to link FFmpeg since two
inline functions defined in avfilter.h will have undefined references
to non-inline libavfilter functions.



git-svn-id: file:///var/local/repositories/ffmpeg/trunk@15665 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b