[MERGE] Support for Putty SSH implementation

[John Whitley]

Dmitry Vasiliev wrote:
> The attached patch adds support for Putty's plink SSH  
> implementation. Also slightly refactored SSH negotiation code and  
> added some tests.

That's just fantastic.  Cygwin ssh setup isn't that big of a deal for  
folks with a strong *nix background, but it can be a fiddly and  
annoying process for folks not familiar with that world.  plink  
support is definitely handy, and I see it being a plus towards Bazaar  
adoption in many Windows shops.

Очен Хорошо!
John