Keyframe-accurate mp4 file cutting

I've done some modifications to the mp4clip tool (part of the MPEG4ip software package) to do key frame accurate cutting/clipping of mp4 files. In general it seems to work, but from time to time it corrupts the source (!) files. Need to find time for debugging.

I'll release the patch as soon I consider it to be used safely. Don't want to be responsible for corrupting someones video collection...