docs/plugins/: Update element args.

docs/plugins/: Update element args.

Original commit message from CVS:
* docs/plugins/gstreamer-plugins.args:
* docs/plugins/inspect/plugin-coreelements.xml:
* docs/plugins/inspect/plugin-coreindexers.xml:
Update element args.
* gst/gstsystemclock.c:
Small comment update.
* plugins/elements/gsttee.c: (gst_tee_class_init), (gst_tee_init),
(gst_tee_request_new_pad), (gst_tee_release_pad),
(gst_tee_buffer_alloc), (gst_tee_sink_activate_push),
(gst_tee_sink_activate_pull):
* plugins/elements/gsttee.h:
Some tee loving:
Add default property defines.
Implement release pad function.
Give properties better blubs etc.
Activate pads before adding them to a running tee.
Do simple buffer_alloc on the first requested pad.
Post error when activation fails.