s3:pam_smbpass: don't call openlog() or closelog() from pam_smbpass

s3:pam_smbpass: don't call openlog() or closelog() from pam_smbpass

Patch from Steve Langasek with tiny fixes by me to make it apply to master.
Also see Debian bug #434372 and bugzilla #4831.

Calling openlog() or closelog() inside a pam module is not good as these
functions are not stackable and no program won't re-do openlog() just because a
pam module might have called closelog().
(cherry picked from commit 5c34ea94bdf9e3efb6743e52dd3c0c0088cff7d8)