libpam: Additional module directory.

Many if not most ports that install PAM modules install them into
${LOCALBASE}/lib/security instead of just ${LOCALBASE}/lib, because
all the world is Linux.  Rather than try to fix the ports, add that
directory to the search path.

MFC after:	1 week
Relnotes:	yes
Reviewed by:	delphij
Differential Revision:	https://reviews.freebsd.org/D50626

contrib/openpam/lib/libpam/openpam_constants.c

@@ -181,11 +181,13 @@ const char *openpam_module_path[] = {
 	"/usr/lib" COMPAT_libcompat,
 #ifdef LOCALBASE
 	LOCALBASE "/lib" COMPAT_libcompat,
+	LOCALBASE "/lib" COMPAT_libcompat "/security",
 #endif
 #else
 	"/usr/lib",
 #ifdef LOCALBASE
 	LOCALBASE "/lib",
+	LOCALBASE "/lib/security",
 #endif
 #endif
 	NULL