libs/gst/base/gstbasesrc.c: Allow sending EOS to the source to make it send out an EOS event from the streaming thread.

Original commit message from CVS:
* libs/gst/base/gstbasesrc.c: (gst_base_src_send_event),
(gst_base_src_get_range), (gst_base_src_pad_get_range),
(gst_base_src_loop), (gst_base_src_set_flushing),
(gst_base_src_change_state):
Allow sending EOS to the source to make it send out an EOS event from
the streaming thread.
Update docs and deprecate the old NULL/READY shutdown method.
* tests/check/libs/basesrc.c: (GST_START_TEST),
(gst_basesrc_suite):
Add unit test for controlled shutdown.