[PATCH 0/4] Bug fixes for identity handling in Emacs

[Austin Clements]

This series fixes several bugs surrounding identity handling in Emacs.
It was inspired by a problem that bjonnh on IRC had where forwarding
from an address where the full name matched the mailbox would crash
`notmuch-mua-new-forward-message'.  While it was possible to work
around that specific problem with a simple fix, it revealed that the
code was subtly broken in many ways.

The patches in this series are all technically independent and can be
pushed in any order, but they're all related problems.