RFC 6: Overall cleanups again.

- License should be fixed now (finally)
- Added doxygen comments
- Cleaned up the X11Grab structure
- Renamed X11Grab structure to x11_grab_s
- Changed some Java stylish named functions to more C'stylish ones
- Changed order of some parameters so they are more libc alike with
  destination as first parameter
- Use AVRational where relevant
- Fixed time calculation
- Cleaned up a few little tiny things around the sources
  + removed a goto
  + removed unused vars
  + etc...

Originally committed as revision 7299 to svn://svn.ffmpeg.org/ffmpeg/trunk