Just like we do with GObject types and G_DEFINE_TYPE, we should
use the g_once_init_enter/g_once_init_leave mechanism to make the
GType registration of enumeration types thread safe.
* clutter/clutter-color.c:
* clutter/clutter-event.c:
* clutter/clutter-stage.c: Intern more strings using the I_() macro
* clutter/clutter-enum-types.c.in: Call g_intern_static_string()
in the enum types template
* clutter/Makefile.am:
* clutter/clutter-enum-types.h.in:
* clutter/clutter-enum-types.c.in: Use template files for
glib-mkenums; this makes the Makefile template a bit more
clean and the enum types generation more customisable (e.g.
when GLib 2.14 has been released, we can use g_once_init_enter()
and g_once_init_leave() to have thread-safe GType functions
for the enum types as well).
