gst/: Implement gst_pad_pause/start/stop_task(), take STREAM lock in task function.

gst/: Implement gst_pad_pause/start/stop_task(), take STREAM lock in task function.

Original commit message from CVS:
* gst/base/gstadapter.c: (gst_adapter_peek), (gst_adapter_flush):
* gst/base/gstbasesink.c: (gst_basesink_preroll_queue_push),
(gst_basesink_finish_preroll), (gst_basesink_chain),
(gst_basesink_loop), (gst_basesink_activate),
(gst_basesink_change_state):
* gst/base/gstbasesrc.c: (gst_basesrc_do_seek),
(gst_basesrc_get_range), (gst_basesrc_loop),
(gst_basesrc_activate):
* gst/elements/gsttee.c: (gst_tee_sink_activate):
* gst/gstpad.c: (gst_pad_dispose), (gst_real_pad_class_init),
(gst_real_pad_init), (gst_real_pad_set_property),
(gst_real_pad_get_property), (gst_pad_set_active),
(gst_pad_is_active), (gst_pad_get_query_types), (gst_pad_unlink),
(gst_pad_link_prepare), (gst_pad_link), (gst_pad_get_real_parent),
(gst_real_pad_get_caps_unlocked), (gst_pad_peer_get_caps),
(gst_pad_accept_caps), (gst_pad_get_peer), (gst_pad_realize),
(gst_pad_event_default_dispatch), (gst_pad_event_default),
(gst_pad_dispatcher), (gst_pad_query), (gst_real_pad_dispose),
(gst_pad_save_thyself), (handle_pad_block), (gst_pad_chain),
(gst_pad_push), (gst_pad_get_range), (gst_pad_pull_range),
(gst_pad_send_event), (gst_pad_start_task), (gst_pad_pause_task),
(gst_pad_stop_task):
* gst/gstpad.h:
* gst/gstqueue.c: (gst_queue_handle_sink_event), (gst_queue_chain),
(gst_queue_loop), (gst_queue_src_activate):
* gst/gsttask.c: (gst_task_init), (gst_task_set_lock),
(gst_task_get_state):
* gst/gsttask.h:
* gst/schedulers/threadscheduler.c:
(gst_thread_scheduler_task_start), (gst_thread_scheduler_func):
Implement gst_pad_pause/start/stop_task(), take STREAM lock
in task function.
Remove ACTIVE pad flag, use FLUSHING everywhere
Added _pad_chain(), _pad_get_range() to call chain/getrange
functions.
Add locks around IS_FLUSHING when reading.
Take STREAM lock in chain(), get_range() functions so plugins
don't need to take it anymore.