* lisp/emacs-lisp/package.el (package-import-keyring)
(package--check-signature-content, package-check-signature):
Use new variable package-gnupghome-dir to control which GnuPG
homedir to use.
* doc/emacs/package.texi: Mention package-gnupghome-dir.
* etc/NEWS: Mention package-gnupghome-dir.