auth/factotum: fix password prompt hang

Fixes #51.

R=rsc
http://codereview.appspot.com/3431044

src/cmd/auth/factotum/main.c

@@ -26,8 +26,6 @@ threadmain(int argc, char *argv[])
 	char *mtpt;
 	char err[ERRMAX];
 
-	rfork(RFNOTEG);
-
 /*	mtpt = "/mnt"; */
 	mtpt = nil;
 	owner = getuser();
@@ -72,6 +70,8 @@ threadmain(int argc, char *argv[])
 	if(argc != 0)
 		usage();
 
+	rfork(RFNOTEG);
+
 	if(trysecstore && havesecstore()){
 		while(secstorefetch() < 0){
 			rerrstr(err, sizeof err);