gstsystemclock: mark the clock as leaking, improve gstcheck docs
commit e484fbbd:
gstsystemclock: Mark the clock as MAY_BE_LEAKED
It is freed in gst_deinit(), but otherwise it is leaked.
commit a16501e5:
gstcheck: Document strcmp used in string cmp macros
strcmp() does not allow the arguments to be NULL, but g_strcmp0()
does, so document that we use g_strcmp0() so that people don't need to
worry about that.