[Dovecot] pop3_lock_session and mdbox format

[Ewald Dieterich]

Setting "pop3_lock_session = yes" in the configuration has no effect
when I use Dovecot 2.1.13 with the mdbox format. A second POP3 
connection to the same mailbox is still allowed.

Grepping for MAILBOX_FLAG_KEEP_LOCKED in the source code shows that
POP3 session locking only works for the Maildir and mbox formats. Is
it possible to enable it for the mdbox format, as well?

Ewald