Use LOGNAME to get current user and fall back to whoami if
not set. Mainly to benefit -portable since some platforms don't have whoami.
Upstream-Regress-ID: e3a16b7836a3ae24dc8f8a4e43fdf8127a60bdfa
Add regression test for AllowUsers and DenyUsers. Patch from
Zev Weiss <zev at bewilderbeest.net>
Upstream-Regress-ID: 8f1aac24d52728398871dac14ad26ea38b533fb9