Just two fixes:

• dovecot-uidlist file is now assumed to be changed if it's modify time is changed. before we relied on inode changing which isn't fully reliable.
• mbox dotlocks sometimes incorrectly thought someone else had overridden them

Known problems that I should fix:

• mbox: we don't necessarily notice message flag changes by external programs (or another dovecot without index files). It's because we don't always reparse the whole mbox file when it has changed. I think I'll have to add some X-IMAP-Changelog header which describes what changes were made by other Dovecot processes. If the change isn't listed in that header, we'll fallback to reparsing the whole file. Although that's still a bit annoying since MTA just appends the new mails, we wouldn't really need to reparse the whole file then, just the new mails.
• I should use link() instead of relying on O_EXCL which doesn't work with NFSv2 (or Linux's NFSv3 client).
• .subscriptions and .customflags files still aren't NFS-safe