Fix "fasthalt" to halt instead of reboot

fasthalt has behaved like reboot, instead of like halt, since r228408
(2011, 10.0-RELEASE).  Fix it.  One wonders if anyone will notice.

Approved by:	re (kib)
MFC after:	3 days
Sponsored by:	Dell EMC Isilon

sbin/reboot/reboot.c

@@ -73,7 +73,7 @@ main(int argc, char *argv[])
 	u_int pageins;
 	const char *user, *kernel = NULL;
 
-	if (strcmp(getprogname(), "halt") == 0) {
+	if (strstr(getprogname(), "halt") != NULL) {
 		dohalt = 1;
 		howto = RB_HALT;
 	} else