Added Linux-PAM and updated description.

Signed-off-by: Nikos Mavrogiannopoulos <nmav@gnutls.org>

libs/libpam/files/pam.d/common-account

@@ -0,0 +1,20 @@
+#
+# /etc/pam.d/common-account - authorization settings common to all services
+#
+# This file is included from other service-specific PAM config files,
+# and should contain a list of the authorization modules that define
+# the central access policy for use on the system.  The default is to
+# only deny service to users whose accounts are expired in /etc/shadow.
+#
+
+# here are the per-package modules (the "Primary" block)
+account	[success=1 new_authtok_reqd=done default=ignore]	pam_unix.so 
+# here's the fallback if no module succeeds
+account	requisite			pam_deny.so
+# prime the stack with a positive return value if there isn't one already;
+# this avoids us returning an error just because nothing sets a success code
+# since the modules above will each just jump around
+account	required			pam_permit.so
+# and here are more per-package modules (the "Additional" block)
+
+# end of pam-auth-update config