bug - over system quota and dovecot-uidlist

[krzf83@gmail.com]

Ever since I've migraded from courier pop3 to dovecot pop3 I'm
constantly getting complains from users that went over system quota
for short while and then their pop3 client downloads all messages
again. I never happened with courier pop3. I think that dovecot does
not handle dovecot-uidlist file safely so it can withstand such
situations.
rsync and other similar programs always writes to a copy of the file
like dovecot-uidlis.xcb453 and on success unlinks old file and renames
new one. Dovecot should not assume that write operation on
dovecot-uidlist will succeed.
Yes, I know I can put metadata like dovecot-uidlist somewhere else, on
another partition but that really splits mailbox into multiple
locations making for example backups way harder to make, restore,
share etc.