* gnu/system/pam.scm (unix-pam-service): Add account and session PAM entries
for pam-gnupg. Don't pass "#f" to "allow-root?" argument, because "lambda*"
already does this by default.
* doc/guix.texi (X Window): Document this.
* gnu/services/xorg.scm (<slim-configuration>)[gnupg?]: New record field.
(slim-pam-service): Pass "#:gnupg?" argument to "unix-pam-service".