Configureable timout for applications to close their windows.

Fix 5sec stall when switching from an application to be stopped to an application that was stopped before.
Make Xinstance thread safe

argpopt.h

@@ -23,6 +23,7 @@
 struct Config
 {
     bool ignoreClientMachine = false;
+    int  timeoutSecs = 10;
 };
 
 const char *argp_program_version = "1.0.4";
@@ -33,6 +34,7 @@ static char args_doc[] = "";
 static struct argp_option options[] = 
 {
   {"ignore-client-machine",  'i', 0,      0,  "Also stop programs associated with windows that fail to set WM_CLIENT_MACHINE" },
+  {"timout", 't', "seconds",      0,  "Timeout to give program to close its last window before stoping it" },
   { 0 }
 };
 
@@ -45,6 +47,9 @@ error_t parse_opt (int key, char *arg, struct argp_state *state)
         case 'i':
         config->ignoreClientMachine = true;
         break;
+        case 't':
+        config->timeoutSecs = atol(arg);
+        break;
         default:
         return ARGP_ERR_UNKNOWN;
     }