bash/prompt: read $PRETTY_HOSTNAME from /etc/machine-info
bash/prompt: skip slow exact-tag matching

Admittedly it's only slow immediately after boot, but that's when it
annoys me the most (~/src/linux means lots of reboots).
dotfiles: add some mailx documentation
mail/nailrc: forget ~/.auth

I will use the new 'agent' support later, I think. Or I might change
this into a local-only option. It doesn't work right now anyway (asks
for a password).

(Not that I _use_ mailx anyway, just have it for that 80's feel.)
mail: add stub ~/.mailrc
mail: merge mailrc and nailrc

I don't really use nail/s-nail, but I *really* never use the old Mailx.
mailrc: set $sendmail for everything, as $smtp overrides it
mailrc: fix Gmail SMTP settings
mailrc: add work account
msmtp: update TLS settings for work account
bash/prompt: _show_status: show signal name
k5login: update
mailrc: set v15-compat, bring back the .auth file for now
git/config: add tig 2.x settings