pad: improve context passing some more
pad: improve context passing some more

Pass the context downstream when it got updated.
Have two ways of informing downstream of events, do a full context update when
the CONTEXT_PENDING flag is set and simply forward the event otherwise.
Set the CONTENT_PENDING flag when linking pads.
We don't need to old context anymore when updating the context of a pad.

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