Enable Windows users with SSH installed to use 'vagrant ssh'

Hello Mitchell,

I think vagrant is awesome, thank you.

I use vagrant on Windows and discovered that 'vagrant ssh' just leads to an error message that says 'use putty'. But I already have ssh on my system because it is included with git (and cygwin, and mingw). So I changed the vagrant code so that it works more like the *nix version and uses "which" to discover whether ssh is already installed. This required that I write a platform independent "which" function in Ruby and some unit tests. And I tested it on Windows and Linux (Ubuntu Lucid).

I hope you like it; please let me know if there's anything you'd like me to change and I will gladly do so.

Best,

Pat
--
Patrick Wyatt - "webcoyote"