based on patch by Yorn <yorn AT gmx.net>

- use variable for destination colorspace

  patch by Juergen Weigert <jw AT suse.de>

* prevent buffer overflows / crashes when handling filenames that are
   too long
* do not allow user-supplied strings in format strings
* more consistent, and sometimes corrected (and nicer :)) error messages
* no more rindex(), it is deprecated and strrchr() is ANSI C and in the
   POSIX standard. I'm absolutely positive that all your supported
   platforms have it (and not only Windows.)

and granulerate denominator was incorrect for vorbis stream.

Fixes #939

- the maximum videobitrate in theora alpha 6 is 2^24-1 (16778 kb/s), not 16000000; however, if we set a bigger value, libtheora accept and truncate it, so I put in the help the value of 16778, but accept also bigger values, e.g. for future versions;
- updated info on preview settings;
- reduced number of lines of ffmpeg2theora -h, while using a maximum of 80 coloumns;

-P | --pid command line option which allows
ffmpeg2theora to register its process id in a file.

- also call ogg_stream_flush on audio stream

though.

  dont create theora pages with more than 23 packets.
this is only relevant for monochrom/static scenes, like back with little txt.
resuling files are a bit bigger, but seeking is faster.
tested with: 
  vlc, totem-gstreamer, wmp9(illi's ds filters)

(use ogg_stream_flush instead of ogg_stream_pageout for theora)

also playback now works for longer black parts with illi's ds decoder, 
possibly there is a way to do this better, patches are welcome.