Don't create invalid maildir names with lower case maildir flags
Don't create invalid maildir names with lower case maildir flags

If someone had a custom :2,a flag, adding a new flag would lead to the
invalid maildir filename ...a:2,... due to regex deficiencies not coping
with this. Fix this so we alway produce valid maildir names.

Note that custom flags are still problematic: as the syncing to the
remote IMAP server will fail, the next sync will assume that they have
been removed from the remote IMAP side and they will be removed from the
local Maildir then. We will need to think about how to handle this. At
least, with this patch we won't lose standard flags and won't produce
invalid maildir names.

Signed-off-by: Sebastian Spaeth <98dcb2717ddae152d5b359c6ea97e4fe34a29d4c@SSpaeth.de>

frioux/offlineimap,frioux/offlineimap