Different tmpdir settings for drafts and attachments

Mutt effectively deals with two different types of temporary files:

1. volatile files, such as attachments passed to MIME viewers;
2. non-volatile files, such as e-mail drafts;

However, there is only one tmpdir setting, which does not properly address both of these types of temporary files:

1. If I set this to /tmp, then I risk that a draft may be cleaned out if the computer crashes, and /tmp is cleared on boot. Thus, drafts should really be stored in /var/tmp;
2. If I use tmpdir=/var/tmp, then /var/tmp ends up being cluttered with truly temporary files, such as attachments passed to auto viewers. Those files should actually go to /tmp;

It would be really useful to be able to define two different locations for these types of files. I already raised this issue almost 10 years ago, and it was forwarded to Trac bug #3236. Given the fact that it has since been forgotten, I am filing the issue here anew.