ssecurity/pam_ssh_agent: New port

pam_ssh_agent is a PAM module for authenticating using ssh-agent.

A PAM authentication module determining the identity of a user based
on a signature request and response sent via the ssh-agent protocol to
a potentially remote ssh-agent.

This project is a re-implementation of the pam_ssh_agent_auth module
but does not share any code with that project. We are pretty close to
covering all the features of the original implementation, along with
some additional features such as authentication using SSH
Certificates.

See also: security/pam_rssh security/pam_ssh_agent_auth