Reinstallation attempted to re-run itself

[alexcrichton]

I've got a few downloads of multirust-rs.exe in my downloads folder, so when I download a new one it's auto-renamed to multirust-rs(N).exe, but the installer only works if the filename is called multirust-rs.exe. Perhaps some extra pattern matching could be in play?

[Diggsey]

This is fixed, just need to add a test.