agent: Support ssh-agent extensions for environment variables.
* common/session-env.c (session_env_list_stdenvnames): Extend to allow return all names as one string. * agent/command-ssh.c (SSH_REQUEST_EXTENSION): New. (SSH_RESPONSE_EXTENSION_FAILURE): New. (request_specs): Add handler for the extension command. (ssh_handler_extension): New.
The extension mechanism is specified in
https://tools.ietf.org/html/draft-miller-ssh-agent-04
- Signed-off-by: Werner Koch <wk@gnupg.org>