Some enhancements for pam_namespace

[Tomas Mraz <tmraz redhat com>]

I've implemented some enhancements for pam_namespace which can be used
for temporary logons. These enhancements were proposed by Dan Walsh.
Please review if you're interested.
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=241226
https://bugzilla.redhat.com/bugzilla/attachment.cgi?id=155825

-- 
Tomas Mraz
No matter how far down the wrong road you've gone, turn back.
                                              Turkish proverb