Add where.exe

What do you think about adding that to the ros tree?
http://www.malsmith.net/which/
http://www.malsmith.net/download/?obj=which/latest-stable/which-source.zip
MIT licensed. Very small. Looks like we were being allowed to import and to change.
E.g. kicking out the msupd.h/.c and keeping only which.c?

Yes, it's a feature that is not present in 2k3sp2 yet. But it's small, neat and dependency-free, and e.g. Win10 does have it. Would anyone oppose?