debian/watch: Version based on file timestamp

[Patrick Matthäi <pmatthaei@debian.org>]

Hi,

for the geoip-database package I would like to add a watch file. The 
problem is: there are no real releases, so I am manualy monitoring the 
required files.

Is it possible to get the upstream version of the remote file based on 
it's modified tag? e.g.:
http://geolite.maxmind.com/download/geoip/database/GeoIPCountryCSV.zip

The required format is: YYYYMMDD
--
/*
Mit freundlichem Gruß / With kind regards,
 Patrick Matthäi
 GNU/Linux Debian Developer

  Blog: http://www.linux-dev.org/
E-Mail: pmatthaei@debian.org
        patrick@linux-dev.org
*/