attribute_manager supports attribute_handler's to handle configuration attributes via plugins

moved resolv.conf editing to a separate plugin (resolv_conf)
extended attribute_provider interface to hand out arbitrary attributes
  moved strongswan.conf based dns/nbns configuration to a plugin (attr)

src/charon/plugins/attr/attr_plugin.h

@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2009 Martin Willi
+ * Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program 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 General Public License
+ * for more details.
+ *
+ * $Id$
+ */
+
+/**
+ * @defgroup attr attr
+ * @ingroup cplugins
+ *
+ * @defgroup attr_plugin attr_plugin
+ * @{ @ingroup attr
+ */
+
+#ifndef ATTR_PLUGIN_H_
+#define ATTR_PLUGIN_H_
+
+#include <plugins/plugin.h>
+
+typedef struct attr_plugin_t attr_plugin_t;
+
+/**
+ * Plugin providing configuration attribute through strongswan.conf.
+ */
+struct attr_plugin_t {
+	
+	/**
+	 * implements plugin interface
+	 */
+	plugin_t plugin;
+};
+
+/**
+ * Create a attr_plugin instance.
+ */
+plugin_t *plugin_create();
+
+#endif /** ATTR_PLUGIN_H_ @}*/