gst/base/gstbasesink.*: Handle newsegments more correctly.

gst/base/gstbasesink.*: Handle newsegments more correctly.

Original commit message from CVS:
* gst/base/gstbasesink.c: (gst_base_sink_handle_object),
(gst_base_sink_event), (gst_base_sink_do_sync),
(gst_base_sink_handle_event):
* gst/base/gstbasesink.h:
Handle newsegments more correctly.

* gst/gstbus.c:
Fix docs.

* gst/gstevent.c: (gst_event_new_newsegment):
A newsegment cannot have a start_time of -1