gst/: define NO_IMPORT_PYGOBJECT to have a correct extern declaration reenable _pygst_element_init and ifdef it corre...

Original commit message from CVS:
* gst/pygstvalue.c:
* gst/gst-argtypes.c:
* gst/gst.override:
define NO_IMPORT_PYGOBJECT to have a correct extern declaration
reenable _pygst_element_init and ifdef it correctly
* gst/arg-types.py:
check errors
* gst/gstcaps.override:
- remove list append functionality. Sets don't support the +
operator
- implement richcompare and coerce, nonzero, or, xor and subtract
number functions
* testsuite/test_caps.py:
add tests for the new stuff