playbin: add support for loading subtitles after playback has started
Submitted by Bastien Nocera @hadess
Link to original bug (#589515)
Description
+++ This bug was initially created as a clone of Bug 514050 +++
Using the patches in Bug 514050 comment 5, playbin2 should be able to load text subtitles on the fly.
But no subtitles are displayed when using this method.