game-data-packager 36/experimental: q2 mission pack support

[Jonathan Dowland <jmtd@debian.org>]

Hi folks,

I uploaded game-data-packager version 36 to experimental. The main
change from 35 is support for the two main Quake II mission packs.
These are implemented as separate top level targets. I plan for the
main "quake2" target to generate mission pack .debs too, if it
detects the data when packaging quake2 data.

I'd like to apply the same model to quake 1 mission packs, as well
as hexen2 once support for præevus is written.

Asides from the above, there are a few small tweaks elsewhere: I
implemented a package_installed() routine to check for the presence
of a binary and complain if it isn't available; this has been hooked
into a lot of targets: lgeneral, quake, quake2, wolf3d and the new
q2 mission packs.