Reset text-position when updating text.

  This updates #210.
  Allow text-mode to get/set the line offset.

  This closes #210.
  Update the maildirs when changing mail_prefix.

  This updates #209.

  (Probably closes it too, but there does seem to be some confusion..)
  Don't update maildirs unnecessarily.

  This closes #209.
  Fixed silly thought-o.

  This allows the code to compile, and work.