gst/gstplugin.c: Fix old-style static plugins via GST_PLUGIN_DEFINE_STATIC again, which I broke two commits ago when ...

Original commit message from CVS:
* gst/gstplugin.c: (_gst_plugin_initialize):
Fix old-style static plugins via GST_PLUGIN_DEFINE_STATIC
again, which I broke two commits ago when changing the API
of gst_plugin_register_static(): the g_list_foreach() in
_gst_plugin_register_static still assumed the old function
signature and would therefore fail (re-fixes #510187).
* gst/gstplugin.c: (_num_static_plugins), (_static_plugins),
(_gst_plugin_register_static), (gst_plugin_register_static):
Revert the (technically correct) change to call g_thread_init() from
the pre-main() constructor. This will break programs which call
g_thread_init() without an if (!g_thread_supported()) guard in their
main function. We could just blame it on GLib or the application, but
it's probably best to just avoid this altogether and simply not use
any GLib functions here and use plain old malloc() with a simple
array...