libssh code contributions

[Gearoid Murphy]

Hi,

We've updated our local build of libssh with some simple additions for 
exposing client public key functions. This allows developers to 
implement arbitrary types of public key authentication without having to 
go into the guts of the (elegantly written) libssh code.

We've also extended the examples with an x509 public authentication demo 
using OpenSSL x509 functions on Linux and WinCrypt certificate functions 
on Windows.

How do we go about pushing this code back into the mainline?, I vaguely 
recall some references to a certification process that's required before 
making commits.

Thanks
 - Gearoid