basetransform: rework accept-caps
basetransform: rework accept-caps

According to the design docs:
The ACCEPT_CAPS query is not required to work recursively, it can simply
return TRUE if a subsequent CAPS event with those caps would return
success.

So make it a shallow check instead of recursivelly check downstream.

https://bugzilla.gnome.org/show_bug.cgi?id=748635

StreamUtils/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,krichter722/gstreamer,centricular/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,centricular/gstreamer,centricular/gstreamer,jpxiong/gstreamer,centricular/gstreamer,krichter722/gstreamer