* For certain IMAP outputs (such as BODYSTRUCTURE), buffer all output until

* For certain IMAP outputs (such as BODYSTRUCTURE), buffer all output until
  we've got the whole thing, then spew it all at once to avoid lots of
  tiny TCP packets.
* New API calls buffer_output() (to start buffering) and unbuffer_output()
  (to dump the buffer and stop buffering) are available to do this.