Support non-relative game detection

[Adrianilloo]

Per the nearby code here, MM detects the game based on relative names (e.g hl2mp). When one wishes to pass absolute paths to the SRCDS -game parameter (which I had the need to do recently), I believe that's a perfectly server invocation but MM might detect the wrong mod and thus load the incorrect extensions, etc.

I think the parsing should manually figure out the mod name by extracting the last path component.