show_config fails because of wrong import

[Jens KLEIN]

show_config fails, the following corrects it (against todays bzr branch)

=== modified file 'src/mailman/bin/show_config.py'
--- src/mailman/bin/show_config.py 2009-01-01 22:16:51 +0000
+++ src/mailman/bin/show_config.py 2009-02-24 18:50:22 +0000
@@ -20,7 +20,7 @@
 import pprint
 import optparse

-from mailman.configuration import config
+from mailman.config import config
 from mailman.i18n import _
 from mailman.version import MAILMAN_VERSION