Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

gnus-art.el (gnus-request-article-this-buffer): Use existing function `gnus-refer-article-methods'.
auth-source.el: Require EPA and EPG.
 (auth-source-passphrase-alist): New variable.
 (auth-source-passphrase-callback-function, auth-source-token-passphrase-callback-function): Callbacks for the netrc field encryption (GPG tokens).
 (auth-source-epa-extract-gpg-token, auth-source-epa-make-gpg-token): Symmetric encryption and decryption of the netrc GPG tokens.
 (auth-source-netrc-normalize): Use them, simplifying the closure.