gst/gstpad.c: throw an error if the getcaps function does not return a subset of...

gst/gstpad.c: throw an error if the getcaps function does not return a subset of the template caps.

Original commit message from CVS:
* gst/gstpad.c: (gst_pad_get_caps):
throw an error if the getcaps function does not return a subset of
the template caps.
* libs/gst/bytestream/filepad.c: (gst_file_pad_chain):
make disconts without position info an error in debugging
* tests/spidey_bench.c: (handoff), (main):
don't count first try when averaging