RLG-Web: improve taking over sessions.

WebSocket sessions should not be taken over, and polling sessions are
not yet convertible to WebSockets.  Eventually the current method of
taking over via Player#reset() should be replaced with autosaving the
game, which will always work.

rlgterm.js

@@ -417,6 +417,10 @@ function setup() {
     else
       break;
   }
+  if (!WebSocket) {
+    message("Your browser does not support WebSockets. You can still play, " +
+            "but it will be slower, and may not work in the future.", "warn");
+  }
   return;
 }
 
@@ -692,8 +696,14 @@ function startgame(game) {
         message("The server forgot about you, please log in again.", "warn");
       }
       else if (reply.c == 4) {
-        message("You can't play that game because it is currently being " + 
-                "played over SSH.", "warn");
+        if (reply.s == "dgamelaunch") {
+          message("You are already playing " + game.name + " over SSH.", 
+                  "warn");
+        }
+        else {
+          message("You are already playing " + game.name + 
+                  " in another browser window.", "warn");
+        }
       }
       else if (reply.c == 7) {
         message("The game is being saved, try again in a few seconds.");

rlgwebd.js

@@ -756,7 +756,7 @@ function startgame(req, res, formdata) {
     var nodematch = new RegExp("^" + username + ":node:");
     if (fname && (fname.match(nodematch) === null)) {
       /* It's being played in dgamelaunch. */
-      sendError(res, 4, null);
+      sendError(res, 4, "dgamelaunch");
       tslog("%s is already playing %s", username, gname);
       return;
     }
@@ -786,7 +786,9 @@ function startgame(req, res, formdata) {
           return;
         }
       }
-      sendError(res, 7);
+      /* If there's no player, it's a WebSocket game, and shouldn't be 
+       * seized. */
+      sendError(res, 4, "WebSocket");
     }
     else {
       new Player(gname, lkey, dims, respondlaunch);