Use g_once when registering enumeration types
Use g_once when registering enumeration types

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.

Distrotech/cogl,Distrotech/cogl,collects/cogl,gcampax/cogl,djdeath/cogl-android,Distrotech/cogl,djdeath/cogl-android,gcampax/cogl,gcampax/cogl,djdeath/cogl,Distrotech/cogl,gcampax/cogl,spatulasnout/cogl,spatulasnout/cogl,djdeath/cogl,collects/cogl,djdeath/cogl-android,djdeath/cogl