AnbPam

As pam uses syslog anchored the prefix as a syslog prefix.

Pam pre 0.99.2.0 (https://git.fedorahosted.org/cgit/linux-pam.git/commit/modules/pam_unix/support.c?id=f0f9c4479303b5a9c37667cf07f58426dc081676) uses the service(pam_unix) or pam_unix as the syslog service name. It was a bit tricky so I removed support for this and left it as a comment.