Don't return but _exit after failed exec*() and fork()

Quoting POSIX[0]:
"Care should be taken, also, to call _exit() rather than exit() if exec cannot be used, since
exit() flushes and closes standard I/O channels, thereby damaging the parent process' standard
I/O data structures. (Even with fork(), it is wrong to call exit(), since buffered data would
then be flushed twice.)"

[0]: http://pubs.opengroup.org/onlinepubs/009695399/functions/vfork.html

setsid.c

@@ -26,7 +26,8 @@ main(int argc, char *argv[])
 	if (getpgrp() == getpid()) {
 		switch (fork()) {
 		case -1:
-			eprintf("fork:");
+			weprintf("fork:");
+			_exit(1);
 		case 0:
 			break;
 		default:
@@ -39,5 +40,5 @@ main(int argc, char *argv[])
 	savederrno = errno;
 	weprintf("execvp %s:", argv[0]);
 
-	return 126 + (savederrno == ENOENT);
+	_exit(126 + (savederrno == ENOENT));
 }