Add msys openssh package

Build script for msys-openssh using mgwport.
Updated to openssh 6.1p1.

Openssh requires the following packages additional for compilation:
-msys-openssl from https://github.com/t-b/mingwGitDevEnv/tree/msys-openssl
-msys-libzip
-msys-libminires
-msys-libcrypt

With this ssh exectuable git clone reached 30MiB/s over my LAN, the one shipped with msysgit reached 1MiB/s.