Fixed pageant support.

[jarredholman]

Fixed pageant agent forwarding support.

Uses a simpler channel interface since it's not a real socket.

[delano]

Thanks for the pull request. Can you give an example of the usecase it fixes?

[jarredholman]

Pageant currently works for authentication but is broken if you try to use it for agent forwarding.

It fixes the same thing as #66 just in a better way.
Instead of trying to make it more like a socket, I just don't treat it like a real one.

I was using this testcase:

require 'net/ssh'

Net::SSH.start('10.1.248.236', 'jholman', :forward_agent => true) do |ssh|
  puts 'hostname ' + ssh.exec!('hostname')
  puts ssh.exec!('ssh-add -l')
end

With net-ssh master you get this output:

hostname jh-arch
C:/dev/rubydev/winssh/net-ssh/lib/net/ssh/ruby_compat.rb:30:in `select': can't convert Net::SSH::Authentication::Pageant::Socket19 into IO (TypeError)
    from C:/dev/rubydev/winssh/net-ssh/lib/net/ssh/ruby_compat.rb:30:in `io_select'

[jarredholman]

It also fixes #55

[delano]

Awesome, thanks. It also passes all the tests on Ruby 1.9 and 2.0 (#66 did neither).

I'll pull it in and create a release soon.