gst/gstpad.c: Implement default fixation once again, so that gst_pad_fixate() actually does anything at all. This pro...

Original commit message from CVS:
* gst/gstpad.c: (fixate_value), (gst_pad_default_fixate),
(gst_pad_fixate_caps):
Implement default fixation once again, so that gst_pad_fixate()
actually does anything at all. This probably needs to be some
sort of a last resort, and use profile-based fixation first, but
since that doesn't exist yet, this is the best we have. Fixes
visualization in Totem.