renderer: expose CoglOutputs

This adds a cogl_renderer_foreach_output() function that can be used to
iterate the display outputs for a particular renderer.

This also updates cogl-info to use this new api so it can dump out all
the output information.

Reviewed-by: Owen W. Taylor <otaylor@fishsoup.net>

(cherry picked from commit a2abf4c4c1fd5aeafd761f965d07a0fe9a362afc)

cogl/cogl-renderer.c

@@ -631,3 +631,17 @@ cogl_renderer_get_driver (CoglRenderer *renderer)
 
   return renderer->driver;
 }
+
+void
+cogl_renderer_foreach_output (CoglRenderer *renderer,
+                              CoglOutputCallback callback,
+                              void *user_data)
+{
+  GList *l;
+
+  _COGL_RETURN_IF_FAIL (renderer->connected);
+  _COGL_RETURN_IF_FAIL (callback != NULL);
+
+  for (l = renderer->outputs; l; l = l->next)
+    callback (l->data, user_data);
+}