introspection vs gtk_init()

[Colin Walters <walters verbum org>]

In https://git.gnome.org/browse/gtk+/commit/?id=6838861d26bfec9af53438022bd1f5b60bab3bf4

I think we need to avoid get_type() functions requiring any explicit initialization or external resources; we 
definitely don't want to require an X server for builds that use introspection.

See: https://bugzilla.gnome.org/show_bug.cgi?id=696457 for an earlier variant.  A general pattern here is to 
break out initialization components into GOnce.

Right?