Better solution for version of debian package

The previous hack updated the changelog (from which the package gets its version number) from within the debian/rules file. This was less than ideal since dpkg-buildpackage has already read the old version at that point. 

Instead do this in scripts/debian-update-versions, which is called by ./update. This way, the built debian package will indicate the same version as was last pulled. As an added bonus, when doing an ./update --master, the debian package version is YEAR.MONTH.DAY.COMMIT. This doesn't depend on anything that ./update doesn't already depend upon (echo,sed,git - i.e., nothing Debian specific). However, if you prefer to leave this out of ./update, the Debian build instructions should be changed to include an invocation of the script. 

There are also some tweaks to remove some build dependencies on Hurd and I've added a Recommend:libgl1-mesa-dri (which is necessary to get proper opengl functionality) and Suggest:libaacs0 for blu-ray playback (I would have added bdplus and dvdcss, but there are no Debian-proper packages for those).