gst/: Change GstBuffer private structure element names. (all files)

gst/: Change GstBuffer private structure element names. (all files)

Original commit message from CVS:
* gst/elements/gstfilesrc.c: (gst_filesrc_free_parent_mmap),
(gst_filesrc_map_region):
* gst/gstbuffer.c: (_gst_buffer_initialize),
(_gst_buffer_sub_free), (gst_buffer_default_copy),
(gst_buffer_new), (gst_buffer_create_sub),
(gst_buffer_is_span_fast), (gst_buffer_span):
* gst/gstbuffer.h:
Change GstBuffer private structure element names. (all files)
* gst/gstqueue.c: (gst_queue_init), (gst_queue_getcaps),
(gst_queue_link):
* gst/gstqueue.h:
Implement getcaps/pad_link functions that handle the case where
there are data in the queue.