API: Add gst_caps_merge() and use it in basetransform, fixes #345444 in a better way

API: Add gst_caps_merge() and use it in basetransform, fixes #345444 in a better way

Original commit message from CVS:
* docs/gst/gstreamer-sections.txt:
* gst/gstcaps.c: (gst_structure_is_equal_foreach),
(gst_caps_merge):
* gst/gstcaps.h:
* libs/gst/base/gstbasetransform.c:
(gst_base_transform_transform_caps):
API: Add gst_caps_merge() and use it in basetransform, fixes #345444
in a better way