global: Fix spelling mistakes in comments Original work by @andreasschulze and @jsoref

pop3: Added %{deleted_bytes} variable to pop3_logout_format

example-config: Moved imap_* and pop3_* settings outside protocol section. There's no need to keep them inside protocol {}, and in case of pop3_uidl_format=%m setting it's actually harmful.

pop3: Added pop3_deleted_flag setting.

pop3_lock_session: Use a separate dovecot-pop3-session.lock file instead of mailbox lock. This changes the behavior in a way that it's now possible for IMAP sessions to expunge mails during a POP3 session. But now it's no longer possible for POP3 sessions to hang new mail deliveries.

pop3: Added pop3_uidl_duplicates setting.

example-config: mail_max_userip_connections default is 10, even for pop3. 3 would probably be better, but there's no way to set per-protocol defaults currently.

pop3: Added pop3_fast_size_lookups setting.

pop3: Added %u=old/new UIDL hash to pop3_logout_format. It expands to "<old msg count>/<old hash> -> <new msg count>/<new hash>" or if they're the same, simply "<msg count>/<hash>". The idea is that if previous session's <new hash> doesn't match next one's <old hash> and prev.new_msg_count = next.old_msg_count, it could indicate that the UIDLs changed for some reason. But if they do match and client still redownloaded messages, it's most likely a client side problem. --HG-- branch : HEAD

example-config: Added nn- prefix to *.conf files so the sort ordering makes more sense. This is especially important to get mail_plugins = $mail_plugins example working in protocol sections. --HG-- branch : HEAD