Add two new functions for filler events (which are used to synchronize streams if one of them is not having any data ...

Original commit message from CVS:
* docs/gst/gstreamer-sections.txt:
* docs/gst/tmpl/gstevent.sgml:
* gst/gstevent.c: (gst_event_new_filler_stamped),
(gst_event_filler_get_duration):
* gst/gstevent.h:
Add two new functions for filler events (which are used to
synchronize streams if one of them is not having any data
for a while) without interrupting the actual data-stream.
Basically a no-op.
* gst/gstqueue.c: (gst_queue_init), (gst_queue_getcaps),
(gst_queue_link_sink), (gst_queue_link_src),
(gst_queue_change_state):
Allow for renegotiation while filled. Required for stream
switching while playing.