gst/gstcaps.*: Add simplify function

gst/gstcaps.*: Add simplify function

Original commit message from CVS:
* gst/gstcaps.c: (gst_caps_normalize), (simplify_foreach),
(gst_caps_structure_simplify), (gst_caps_simplify):
* gst/gstcaps.h:
Add simplify function
* gst/gstpad.c: (gst_pad_link_try), (gst_pad_try_set_caps),
(gst_pad_perform_negotiate), (gst_pad_is_negotiated):
* gst/gstpad.h:
Copy over srcnotify, sinknotify when calling old pad_link
functions.  Add new is_negotiated() function.
* gst/gststructure.c: (gst_structure_copy):
Fix an incredibly stupid bug that should have been noticed
weeks ago.  _copy() returned the argument, not the new copy.