RFC 2 stage: First feedback from review comments

- License is GPL, simplify the license header to make it clear
- Add myself to license header, clarify who did what
- Use 64 bit PTS
- Move mouse bitmaps to the mouse cursor painting function. Make them
  const again
- Properly detach X11 from the shared memory segment on close
- Destroy X11 image on close

Originally committed as revision 7296 to svn://svn.ffmpeg.org/ffmpeg/trunk