[imp] Bug Imp 3.1 in rename_sentmail_monthly.php

[Viljo Viitanen]

In 3.1 lib/Maintenance/Task/rename_sentmail_monthly.php, when using certain
locales, where abbreviated month names contain spaces (e.g. in Finnish,
"Jan" is "tammi "), rename fails. (This is using php 4.2.2 and c-client 4.7a
in php and cyrus imapd 1.6.something.)

I worked around that by changing the strftime format to "-%Y-%m", which is
better anyway, IMHO (past sent folders sort chronologically, then).

-- 
Viljo Viitanen