Do not call event_del() for signals after fork(), just use sigaction()

directly instead - calling libevent functions after fork() w/o
event_reinit() is a bad idea, even if in this case it was harmless.

tmux.c

@@ -549,7 +549,7 @@ main(int argc, char **argv)
 
 	event_dispatch();
 
-	clear_signals();
+	clear_signals(0);
 
 	client_main();	/* doesn't return */
 }
@@ -636,7 +636,7 @@ main_dispatch(const char *shellcmd)
 			memcpy(&shelldata, imsg.data, sizeof shelldata);
 			shelldata.shell[(sizeof shelldata.shell) - 1] = '\0';
 
-			clear_signals();
+			clear_signals(0);
 
 			shell_exec(shelldata.shell, shellcmd);
 		default: