Make SetEnv directives first-match-wins in both sshd_config and

Make SetEnv directives first-match-wins in both sshd_config and
sshd_config; previously if the same name was reused then the last
would win (which is the opposite to how the config is supposed to
work).

While there, make the ssh_config parsing more like sshd_config.

bz3438, ok dtucker