mutt: update to 1.5.23

This commit rewrites this expression quite a lot:
- it uses fetchhg instead of fetchurl now.
- it simplifies the structure of the expression
- it patches configure.ac due to missing mail paths on NixOS
Merge branch 'master' of github.com:1126/nixpkgs

Conflicts:
	pkgs/applications/networking/mailreaders/mutt/default.nix