Bug 1070429 - [email/IMAP] premature saving leads to missing bodies

allbackMaker is effectively deprecated; it was a serious design error on my part to let it vary its behaviour based on the number of arguments (or to let it be altered to do that if I was just the reviewer; unsure, don't care) since it leads to ugly complexity like this.

Rather than complicating this method, would it be okay to put a big capital letter warning on allbackMaker to not use it for new code and to make the extractErrFromCallbackArgs very explicit about it only being for use with 'latch'?