Registers gtypes for all public objects and structs

This adds much more comprehensive support for gobject-introspection
based bindings by registering all objects as fundamental types that
inherit from CoglObject, and all structs as boxed types.

Co-Author: Robert Bragg <robert@linux.intel.com>

Reviewed-by: Neil Roberts <neil@linux.intel.com>

cogl/cogl-snippet.h

@@ -341,6 +341,15 @@ typedef struct _CoglSnippet CoglSnippet;
 
 #define COGL_SNIPPET(OBJECT) ((CoglSnippet *)OBJECT)
 
+#ifdef COGL_HAS_GTYPE_SUPPORT
+/**
+ * cogl_snippet_get_gtype:
+ *
+ * Returns: a #GType that can be used with the GLib type system.
+ */
+GType cogl_snippet_get_gtype (void);
+#endif
+
 /* Enumeration of all the hook points that a snippet can be attached
    to within a pipeline. */
 /**