gst_pad_send_event should send the event on the eventhandler instead of the
eventfunction so that the schedulers can insert a custom handler if they
wish. This patch changes this and fixes the bug where a flush event would
not clear the queued buffers in the optimal scheduler (and basic).
Vorbisfile should work reliable again after this patch. This patch also
includes changes to the basic scheduler so that it inserts custom code to
flush the bufpen in case of a seek/flush event.