Remove mentions of ffmpegcolorspace now that it's in gst-plugins-base

Remove mentions of ffmpegcolorspace now that it's in gst-plugins-base

Original commit message from CVS:
* HACKING:
* ext/ffmpeg/gstffmpegcolorspace.c:
Remove mentions of ffmpegcolorspace now that it's in
gst-plugins-base

* ext/ffmpeg/Makefile.am:
Link to gstreamer libraries
* ext/ffmpeg/gstffmpegcodecmap.c: (gst_ffmpeg_caps_to_pixfmt):
* ext/ffmpeg/gstffmpegdec.c: (gst_ffmpegdec_init),
(gst_ffmpegdec_close), (gst_ffmpegdec_setcaps),
(gst_ffmpegdec_negotiate), (gst_ffmpegdec_frame):
Convert to fractional framerate