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.