Call setsid() for hook/notification commands

We do not want hook or notification commands to interact with the
terminal in any way. Create a new session for them.

Addresses GitHub issue #326.

Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

src/hooks.c

@@ -51,7 +51,7 @@ int run_hook(const char *name)
 	arg[0] = hook_path;
 	arg[1] = NULL;
 
-	if ((pid = shell_exec(&pin, &pout, &perr, *arg, arg))) {
+	if ((pid = shell_exec(&pin, &pout, &perr, 1, *arg, arg))) {
 		ret = child_wait(&pin, &pout, &perr, pid);
 		if (ret > 0 && WIFEXITED(ret)) {
 			asprintf(&mesg, "%s hook: exit status %d",