constraint: Add a private header

And move the only private ClutterConstraint method to it.

This commit also sneaks in a change that makes sense for the debugging
of the update_allocation() method, which checks if the allocation was
effectively changed.

clutter/clutter-constraint-private.h

@@ -0,0 +1,35 @@
+/*
+ * Clutter.
+ *
+ * An OpenGL based 'interactive canvas' library.
+ *
+ * Copyright (C) 2010  Intel Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __CLUTTER_CONSTRAINT_PRIVATE_H__
+#define __CLUTTER_CONSTRAINT_PRIVATE_H__
+
+#include "clutter-constraint.h"
+
+G_BEGIN_DECLS
+
+gboolean clutter_constraint_update_allocation (ClutterConstraint *constraint,
+                                               ClutterActor      *actor,
+                                               ClutterActorBox   *allocation);
+
+G_END_DECLS
+
+#endif /* __CLUTTER_CONSTRAINT_PRIVATE_H__ */