Merge branch 'bb/imap-send-openssl-4.0-prep'

"imap-send" used to use functions whose use is going to be removed
with OpenSSL 4.0; rewrite them using public API that has been
available since OpenSSL 1.1 since 2016 or so.

* bb/imap-send-openssl-4.0-prep:
  imap-send: move common code into function host_matches()
  imap-send: use the OpenSSL API to access the subject common name
  imap-send: use the OpenSSL API to access the subject alternative names