pam_unix: Add no_pass_expiry option to ignore password expiration.

pam_unix: Add no_pass_expiry option to ignore password expiration.

* modules/pam_unix/pam_unix.8.xml: Document the no_pass_expiry option.
* modules/pam_unix/pam_unix_acct.c (pam_sm_acct_mgmt): If no_pass_expiry
is on and return value data is not set to PAM_SUCCESS then ignore
PAM_NEW_AUTHTOK_REQD and PAM_AUTHTOK_EXPIRED returns.
* modules/pam_unix/pam_unix_auth.c (pam_sm_authenticate): Always set the
return value data.
(pam_sm_setcred): Test for likeauth option and use the return value data
only if set.
* modules/pam_unix/support.h: Add the no_pass_expiry option.