- extend the plugin system with an event-based callback infrastructure

- implement callback hooks for task state transitions
 - example echo plugin that logs all callback invocations

plugins/echo.py

@@ -0,0 +1,15 @@
+# Example Koji callback
+# Copyright (c) 2009 Red Hat, Inc.
+# This callback simply logs all of its args using the logging module
+#
+# Authors:
+#     Mike Bonnet <mikeb@redhat.com>
+
+from koji.plugin import callbacks, callback, ignore_error
+import logging
+
+@callback(*callbacks.keys())
+@ignore_error
+def echo(cbtype, *args, **kws):
+    logging.getLogger('koji.plugin.echo').info('Called the %s callback, args: %s; kws: %s',
+                                               cbtype, str(args), str(kws))