Enable threads in g_type_init()

This means threads will be supported for all gobject libraries/applications
and initialized early enough to not cause any problems.

This solves the problem of libraries needing threadsafety. Previosly
they just called g_threads_init() anyway, which often works but sometimes
breaks in unexpected ways.

See this thread for more details:
http://mail.gnome.org/archives/gtk-devel-list/2009-November/msg00208.html

https://bugzilla.gnome.org/show_bug.cgi?id=606775

gobject/gtype.c

@@ -4180,7 +4180,12 @@ g_type_init_with_debug_flags (GTypeDebugFlags debug_flags)
   GTypeInfo info;
   TypeNode *node;
   volatile GType votype;
-  
+
+#ifdef G_THREADS_ENABLED
+  if (!g_thread_get_initialized())
+    g_thread_init (NULL);
+#endif
+
   G_LOCK (type_init_lock);
   
   G_WRITE_LOCK (&type_rw_lock);
@@ -4284,6 +4289,8 @@ g_type_init_with_debug_flags (GTypeDebugFlags debug_flags)
  * to initialize the type system and assorted other code portions
  * (such as the various fundamental type implementations or the signal
  * system).
+ *
+ * Since version 2.24 this also initializes the thread system
  */
 void
 g_type_init (void)