* Add frame rate conversion when there is no audio channel. This makes

  ffmpeg/ffserver work again when just capturing video from a live
  source and you are streaming feeds of different frame rates.
* Fix a segfault in argument processing
* Add handling for -vhook argument
* Add logic to call video hooks if any have been specified.

Originally committed as revision 1247 to svn://svn.ffmpeg.org/ffmpeg/trunk