filter deprecation warnings because of deprecated popen2 (LP: #617872)

Index: sid/plugins/dovecot.py
===================================================================
--- sid.orig/plugins/dovecot.py	2012-04-09 16:19:06.904001000 +0100
+++ sid/plugins/dovecot.py	2012-04-09 16:34:06.965175538 +0100
@@ -18,6 +18,9 @@
 ## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 ## USA
 
+import warnings
+warnings.filterwarnings("ignore")
+
 import __init__
 import FileStorage
 import urllib