[PATCH xdm] Support installing systemd unit file.

[Mark Kettenis]

> From: =?UTF-8?q?Micha=C5=82=20G=C3=B3rny?= <mgorny at gentoo.org>
> Date: Wed, 15 Jun 2011 13:59:43 +0200
> 
> Signed-off-by: Michał Górny <mgorny at gentoo.org>
> Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=38339

>  Makefile.am     |   10 ++++++++++
>  configure.ac    |   12 ++++++++++++
>  xdm at .service.in |   10 ++++++++++

Is it really a good idea to have a file with an '@' character in its
name?  It's not in the Portable Filename Character Set defined by
POSIX.