MFC r358065:

The words ALL, LOCAL, and EXCEPT have special meaning and are documented
as in the login.access(5) man page. However strcasecmp() is used to compare
for these special strings. Because of this User accounts and groups with
the corresponding lowercase names are misintrepreted to have special
whereas they should not.

This commit fixes this, conforming to the man page and to how the Linux
pam_access(8) handles these special words.

Approved by: des (implicit, blanket)