gst/gstpad.c: Rearrange/rewrite much of the pad negotiation code, since it resembled...

gst/gstpad.c: Rearrange/rewrite much of the pad negotiation code, since it resembled pasta.  This actually changes th...

Original commit message from CVS:
* gst/gstpad.c:
Rearrange/rewrite much of the pad negotiation code, since it
resembled pasta.  This actually changes the way some
negotiation works, since the previous code was inconsistent
depending on how it was invoked.  Add (internal) structure
GstPadLink, which is used to hold some information (more in
the future) about the link between two pads.  Fixes a number
of bugs, including random lossage of filter caps when the
initial negotiation is delayed.  A few functions are still
unimplemented.
* gst/gstpad.h:
Add GST_PAD_LINK_{SUCESSFUL|FAILED}() macros.  Please use
these when testing GstPadLinkReturn values instead of comparing
directly.