Add missing call to g_type_init()

The Glib docs state "Prior to any use of the type system, g_type_init() has to
be called".[1] To not do so can lead to segfaults.  The g_type system is
currently used by various "filters" that operate on uuencoded text, message
headers, etc.

[1] http://developer.gnome.org/gobject/2.28/gobject-Type-Information.html#g-type-init

notmuch.c

@@ -579,6 +579,7 @@ main (int argc, char *argv[])
     local = talloc_new (NULL);
 
     g_mime_init (0);
+    g_type_init ();
 
     if (argc == 1)
 	return notmuch (local);