Bug#733750: support patching hexen2 game data

[Simon McVittie]

Control: tags -1 = pending

On Thu, 25 Jan 2018 at 14:56:19 +0100, Alexandre Detiste wrote:
> This also confuses GDP which ends up thinking data1/pak*.pak?v1.11 are downloadable.
> It then dowloads gamedata-all-1.29a.tgz for nothing.

Thanks, fixed in git. The code was correctly taking into account the
other_parts of a multi-part archive that is present, but not doing the
same for one that is merely downloadable (and deltas are treated like
the first part of a multi-part archive).

    smcv