To generate a tarball for a new upstream release, change the variables SVNREV
and VERSION in debian/rules and then run

 $ make -f debian/rules get-orig-source

This will generate an upstream tarball in the current directory.

Please also change UPSTREAM_SVNREV to match the upstream release. You can find
the correct value in ground.Outside.pak in the upstream binary release (the
"418:419" in "pak64 110.0 r418:419").
