Removed obsolete comment.
  Declare a new lua-accessible variable "tmp".

  This will hold $TMPDIR, $TMP, or finally /tmp.

  We'll use this for all temporary operations in the future.
  Correctly update flags when replying to mail.

  THis allows mutt to see messages as being "replied" when lumail
 has been used to reply to a mail.

  This fixes #65.