gst/gstpad.c: Propagate errors from _set_caps() in configure_src/sink functions inste...

gst/gstpad.c: Propagate errors from _set_caps() in configure_src/sink functions instead of returning TRUE.

Original commit message from CVS:
* gst/gstpad.c: (gst_real_pad_init), (gst_pad_set_active),
(gst_pad_link_prepare), (gst_pad_link), (gst_pad_accept_caps),
(gst_pad_configure_sink), (gst_pad_configure_src),
(gst_pad_alloc_buffer), (gst_pad_query), (gst_pad_send_event),
(gst_pad_start_task):
Propagate errors from _set_caps() in configure_src/sink
functions instead of returning TRUE.
FLUSH events can travel up and downstream