This commit makes significant changes to pam_login_access(8) to bring it
up to par with the Linux pam_access(8).

Like the Linux pam_access(8) our pam_login_access(8) is a service module
for pam(3) that allows a administrator to limit access from specified
remote hosts or terminals. Unlike the Linux pam_access, pam_login_access
is missing some features which are added by this commit:

Access file can now be specified. The default remains /etc/access.conf.
The syntax is consistent with Linux pam_access.

By default usernames are matched. If the username fails to match a match
against a group name is attempted. The new nodefgroup module option will
only match a username and no attempt to match a group name is made.
Group names must be specified in brackets, "()" when nodefgroup is
specified. Otherwise the old backward compatible behavior is used.
This is consistent with Linux pam_access.

A new field separator module option allows the replacement of the default
colon (:) with any other character. This facilitates potential future
specification of X displays. This is also consistent with Linux pam_access.

A new list separator module option to replace the default space/comma/tab
with another character. This too is consistent with Linux pam_access.

Linux pam_access options not implemented in this commit are the debug
and audit options. These will be implemented at a later date.

Reviewed by: bjk, bcr (for manpages)
Approved by: des (blanket, implicit)
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D23198