gst/elements/: New element that acts like an identity, but filters caps.  Will eventually replace filtered caps in pa...

Original commit message from CVS:
* gst/elements/Makefile.am:
* gst/elements/gstcapsfilter.c: New element that acts like an
identity, but filters caps.  Will eventually replace filtered
caps in pad linking.
* gst/gstutils.c: (gst_element_create_all_pads): New function
to create all the ALWAYS pads that are registered with an
element class.  This functionality should eventually be
merged in with GstElement initialization.
* gst/gstutils.h:
* testsuite/trigger/README: part of trigger test code that should
have been checked in a long time ago.