Emacs 27.1 obsoleted tls.el

[wasamasa]

I've upgraded and got a warning about tls.el being obsoleted. No rush of fixing this one, but in a future release it will be gone. This shouldn't be too hard to fix, things I've found so far:

• tls-end-of-info needs to be vendored. I remember a bug report about it where the regexp has been adjusted and should take a closer look whether the suggested or the most current regexp work better.
• tls-program seems analogous to tls-connection-command, but omits OpenSSLs s_client which caused numerous issues in the past and should most likely not be used. There's at least one bug report about it and it might need adjustment, too.
• tls-process-connection-type and tls-success need to be vendored.
• Finally, (require 'tls) should be dropped and a changelog note about lack of s_client support made.

See also:

• Circe fails silently when gnutls-cli is not present #287
• Default connection to Freenode fails #340 (comment)
• Remove OpenSSL's s_client fallback #315

A more drastic solution would be to use built-in TLS support as suggested in the last link, at the cost of Emacs possibly hanging when reconnecting (an issue not present with the subprocess solution).