[Mingw-cross-env-list] new tool: patch-tool-mingw

[Mark Brand]

 Hi,

I have checked in a script to make it easy to convert between patch 
files and short-lived git repos. This version is newer than the one I 
already shared with some of you.

http://hg.savannah.gnu.org/hgweb/mingw-cross-env/rev/5d51efc6e43a

There's room for improvement, so feel free to criticize, improve, 
rename, etc.

regards,

Mark