bug#24274: 24.5; Use auth-source library for remote passwords in Rmail

[Antoine Kalmbach]

Lars Ingebrigtsen writes:

> I've re-spun the patch for Emacs 28.  Can somebody that uses rmail
> test this?

I can confirm it works. Applied the patch and it works perfectly. Tested with
both passwords in ~/.authinfo and the macOS keychain, the value of auth-sources
was:

   (macos-keychain-generic macos-keychain-internet "~/.authinfo" 
"~/.authinfo.gpg" "~/.netrc")

The version of Emacs used was

   GNU Emacs 27.1 (build 1, x86_64-apple-darwin18.7.0, Carbon Version 158 
AppKit 1671.6) of 2020-08-16

-- 
Antoine Kalmbach