[util/macros] factorize tests for xmlto

[Julien Cristau]

On Sun, Jan  3, 2010 at 18:16:29 +0100, Matthieu Herrb wrote:

> +# XORG_CHECK_XMLTO
> +# ----------------
> +# Minimum version: 1.4.2
> +#

New macro means new minor version, please make this 1.5.0.  Patchlevel
bumps should only fix existing macros.

Thanks,
Julien