baseparse: modify reverse playback handling
baseparse: modify reverse playback handling

... so as to allow the push-mode case to provide data to subclass
on a buffer by buffer basis (as in regular forward case), rather
than all buffers of a fragment chucked together.

Also refactor buffer handling some more, and add some debug.

lubosz/gstreamer,cfoch/gstreamer,shelsonjava/gstreamer,krieger-od/gstreamer,ensonic/gstreamer,Lachann/gstreamer,centricular/gstreamer,ensonic/gstreamer,lovebug356/gstreamer,lubosz/gstreamer,StreamUtils/gstreamer,jpakkane/gstreamer,jpxiong/gstreamer,centricular/gstreamer,jpakkane/gstreamer,mparis/gstreamer,shelsonjava/gstreamer,krieger-od/gstreamer,krieger-od/gstreamer,cablelabs/gstreamer,StreamUtils/gstreamer,surround-io/gstreamer,centricular/gstreamer,surround-io/gstreamer,collects/gstreamer,cablelabs/gstreamer,shelsonjava/gstreamer,ensonic/gstreamer,collects/gstreamer,justinjoy/gstreamer,Lachann/gstreamer,justinjoy/gstreamer,cfoch/gstreamer,krichter722/gstreamer,krichter722/gstreamer,lovebug356/gstreamer,ensonic/gstreamer,jpakkane/gstreamer,Lachann/gstreamer,jpxiong/gstreamer,surround-io/gstreamer,mparis/gstreamer,Lachann/gstreamer,cfoch/gstreamer,StreamUtils/gstreamer,ensonic/gstreamer,surround-io/gstreamer,krieger-od/gstreamer,centricular/gstreamer,jpxiong/gstreamer,collects/gstreamer,jpxiong/gstreamer,cablelabs/gstreamer,lovebug356/gstreamer,cfoch/gstreamer,StreamUtils/gstreamer,cablelabs/gstreamer,lovebug356/gstreamer,justinjoy/gstreamer,krieger-od/gstreamer,krichter722/gstreamer,jpakkane/gstreamer,collects/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,jpakkane/gstreamer,Lachann/gstreamer,mparis/gstreamer,shelsonjava/gstreamer,lubosz/gstreamer,krichter722/gstreamer,justinjoy/gstreamer,cfoch/gstreamer,centricular/gstreamer,lubosz/gstreamer,lubosz/gstreamer,surround-io/gstreamer,mparis/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,cablelabs/gstreamer,collects/gstreamer,lovebug356/gstreamer,krichter722/gstreamer,justinjoy/gstreamer