SMTP connection test

Takes host, port, user and password, and prints the real underlying SMTP error rather than the vague message WordPress mail plugins surface.

Useful on nearly every client site with mail problems.

Lives at projects/throwaway/smtp-check, uses the built-in smtplib, no dependencies.

At risk

Not a git repository. Being a single file, the neatest fix is moving it into the dotfiles bin/ folder alongside updraft-scan.py, which backs it up and puts it on PATH at once.