non-destructively auto-install userpatch

[goto-bus-stop]

To ensure that players all have the same game version, it'd be good to provide (optionally, ideally) a UserPatch installer. This shouldn't overwrite anything (eg. a Vooblyfied aoc should still work with voobly). I'm not sure if running the UP setup on a Vooblyfied aoc works or if it needs an original exe.

If UP setup works on Vooblyfied installs, aocmultiny can just ship a UP setup and run it, and revert to a backup when the game is finished.

Another option is to then move the UP executable to eg. age2_x1.aocmultiny.exe and add a DirectPlay registry entry for it. That might also make switching game types easier in the future (eg. to support exe mods like Forgotten Empires)