gst/gstcaps.c: fix bug when converting from empty string.

gst/gstcaps.c: fix bug when converting from empty string.

Original commit message from CVS:
* gst/gstcaps.c: (gst_caps_from_string_inplace):
fix bug when converting from empty string.
* gst/gstcaps.c: (gst_caps_new_any), (gst_caps_new_simple),
(gst_caps_new_full_valist), (gst_caps_copy), (gst_caps_copy_1):
use gst_caps_new_empty to allocate a new caps. Only that function
allocates memory for caps now.
* gst/gstcaps.c: (gst_caps_remove_and_get_structure),
(gst_caps_remove_structure):
add ability to remove one structure (but not to header yet)
* gst/gstcaps.c: (gst_caps_compare_structures),
(gst_caps_simplify), (gst_caps_structure_figure_out_union),
(gst_caps_structure_simplify), (gst_caps_do_simplify),
* gst/gstcaps.h:
add gst_caps_do_simplify that tries to simplify a caps in place.
Deprecate old gst_caps_simplify function.
* testsuite/caps/caps.h:
add caps.h containing a common set of caps to test against.
* testsuite/caps/sets.c: (check_caps), (main):
use it.
* testsuite/caps/.cvsignore:
* testsuite/caps/Makefile.am:
* testsuite/caps/simplify.c: (check_caps), (main):
add test to check correctness and efficency of caps simplification.