check/gst/gstutils.c: More checks.

check/gst/gstutils.c: More checks.

Original commit message from CVS:
* check/gst/gstutils.c: (GST_START_TEST), (gst_utils_suite):
More checks.

* gst/gstclock.c: (gst_clock_finalize), (gst_clock_set_master),
(do_linear_regression), (gst_clock_add_observation):
Cleanups.
Release lock when the clock cannot be slaved.
Catch the case where the regression returned an invalid denominator.

* gst/gstutils.c: (gst_util_div128_64_iterate),
(gst_util_div128_64), (gst_util_uint64_scale_int64),
(gst_util_uint64_scale), (gst_util_uint64_scale_int):
Add protentially more performant non-iterative 128/64 divide function
that unfortunatly does not work yet.
Shortcut the trivial 0/X = 0 case.
Remove the warnings on overflow.