Improvements to FindFFmpeg.cmake
Improvements to FindFFmpeg.cmake

1. If only a src dir is supplied consider it build dir (in-source tree build)
2. Find uninstalled versions of the libraries if builddir is supplied
3. Find configuration header when ffmpeg is built out of source tree

artm/WatchThatSound,artm/WatchThatSound,artm/WatchThatSound,artm/WatchThatSound