gst/: Fix gst_pad_peer_get_caps(), make it return NULL if no peer.

gst/: Fix gst_pad_peer_get_caps(), make it return NULL if no peer.

Original commit message from CVS:
* gst/base/gstbasetransform.c: (gst_base_transform_proxy_getcaps):
* gst/elements/gstcapsfilter.c: (gst_capsfilter_getcaps):
* gst/gstpad.c: (gst_pad_peer_get_caps):
* gst/gstqueue.c: (gst_queue_init), (gst_queue_getcaps),
(gst_queue_bufferalloc), (gst_queue_handle_sink_event),
(gst_queue_src_activate), (gst_queue_change_state):
* gst/gstqueue.h:
* gst/gstutils.c: (gst_element_get_compatible_pad_template),
(intersect_caps_func):
Fix gst_pad_peer_get_caps(), make it return NULL if no peer.
Always take QUEUE_LOCK after STREAM_LOCK or we might deadlock.
Some fixes for the peer_get_caps() change.