[MERGE] Support for Putty SSH implementation

[Andrew Bennetts]

John Arbash Meinel wrote:
[...]
> > 
> > I don't think this convention is documented anywhere (I don't see it in HACKING
> > or PEP 8), but the other names being imported from bzrlib.errors there are in
> > alphabetical order; I think it would be good to keep that ordering.
> > 
> 
> IIRC, PEP8 says that imports should be in sorted order. I think we just
> took it such that if

I thought PEP 8 said that too, but I cannot find where, so I guess it doesn't.
(It says imports should be grouped in a specific order, but says nothing about
ordering within a group.)

> import bar
> import foo
> 
> is in sorted order, then
> 
> from x import (
>   bar,
>   foo,
>   )
> 
> should also be in sorted order.

That seems sensible to me.  Perhaps it's worth adding to HACKING, seeing as PEP
8 doesn't cover it.

-Andrew.