gst/gstbin.c: Refactor the sort iterator so it can be used while holding the

gst/gstbin.c: Refactor the sort iterator so it can be used while holding the

Original commit message from CVS:
* gst/gstbin.c: (gst_bin_dispose), (gst_bin_provide_clock_func),
(gst_bin_sort_iterator_new), (gst_bin_iterate_sorted):
Refactor the sort iterator so it can be used while holding the
LOCK too.
Make clock selection select a clock closest to the source.