Log Message:
Changes 2.0.9:
* Linux: Fixed a high system CPU usage / high context switch count
  performance problem
* Maildir: Avoid unnecessarily reading dovecot-uidlist while opening
  mailbox.
* Maildir: Fixed renaming child mailboxes when namespace had a prefix.
* mdbox: Don't leave partially written messages to mdbox files when
  aborting saving.
* Fixed master user logins when using userdb prefetch
* lda: Fixed a crash when trying to send "out of quota" reply
* lmtp: If delivering duplicate messages to same user's INBOX,
  create different GUIDs for them. This helps to avoid duplicate
  POP3 UIDLs when pop3_uidl_format=%g.
* virtual storage: Fixed saving multiple mails in a transaction
  (e.g. copy multiple messages).
* dsync: Saved messages' save-date was set to 1970-01-01.