Ticket 468 - if pam_passthru is enabled, need to AC_CHECK_HEADERS([security/pam_appl.h])
Bug Description: There is no check for a required header file in plugins/pam_passthrough/pam_ptimpl.h
Fix Description: Add header file check to configure.ac
https://fedorahosted.org/389/ticket/468
Reviewed by: richm(Thanks!)
(cherry picked from commit dbc0a95e675d8fba1bd4d4910dc01ea4f246f5c6)