The package now has a dependency on a .so, so it's
architecture-specific now. Technically we should split the
architecture-specific and architecture-independent bits into separate
packages, but I don't want to bother with that for a one-off package
script like this.
Doing this rather than depending on Mercurial will allow developers of
Mercurial to have this package installed without having to do
something awkward to not also get Mercurial from their distro.
