Use vfork() instead of fork() before exec()

If running on older Linux systems, or any BSD UNIX, vfork()
is more efficient when we are about to call exec() anyway.

For more info on vfork() vs fork(), see Stack Exchange:
http://stackoverflow.com/questions/4259629/what-is-the-difference-between-fork-and-vfork

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

svc.c

@@ -458,7 +458,7 @@ int svc_start(svc_t *svc)
 	sigaddset(&nmask, SIGCHLD);
 	sigprocmask(SIG_BLOCK, &nmask, &omask);
 
-	pid = fork();
+	pid = vfork();
 	sigprocmask(SIG_SETMASK, &omask, NULL);
 	if (pid == 0) {
 		int i = 0;