gst/gststructure.c: Forward-port a 0.8 patch to handle escaped spaces in structure...

gst/gststructure.c: Forward-port a 0.8 patch to handle escaped spaces in structure string,          so that gst_parse...

Original commit message from CVS:

patch by: Tim-Philipp Müller <tim at centricular dot net>

* gst/gststructure.c: (gst_structure_parse_field),
(gst_structure_from_string):
Forward-port a 0.8 patch to handle escaped spaces in structure string,          so that gst_parse_launch() can deal with spaces in filtered link
caps (fixes #164479)
* check/gst/capslist.h:
* check/gst/gststructure.c: (GST_START_TEST):
add unit tests for this change