[WIP] Get rid of msys in favor of busybox port for windows

Hi,

I'm integrating some code from busybox to mingw tree so that mingw port can work without msys. Posix utilities such as sed, awk, head, tail... seem to work well. The main obstacle is ash, which is no where near usable state (fork issues as always). Busybox ash is about 13000 lines of code, not too big.

Anyone interested in?