Further fixes for fallback error handler

Layout improvements as well as an check for ErrorEvent.error as it is
not standardized.

app/styles/base.css

@@ -205,10 +205,27 @@ input[type=button]:active, select:active {
   visibility: visible;
   opacity: 1;
 }
+
 #noVNC_fallback_errormsg {
   font-weight: normal;
 }
 
+#noVNC_fallback_error .noVNC_location {
+  font-style: italic;
+  font-size: 0.8em;
+  color: rgba(255, 255, 255, 0.8);
+}
+
+#noVNC_fallback_error .noVNC_stack {
+  padding: 10px;
+  margin: 10px;
+  font-size: 0.8em;
+  text-align: left;
+  white-space: pre;
+  border: 1px solid rgba(0, 0, 0, 0.5);
+  background: rgba(0, 0, 0, 0.2);
+}
+
 /* ----------------------------------------
  * Control Bar
  * ----------------------------------------

app/ui.js

@@ -26,16 +26,29 @@ var UI;
     "use strict";
 
     // Fallback for all uncought errors
-    window.addEventListener('error', function(e) {
+    window.addEventListener('error', function(event) {
         try {
-            var file = e.filename;
+            var msg = "";
-            var line = e.lineno;
+
-            var col = e.colno;
+            msg += "<div>";
-            var msg = e.error.message;
+            msg += event.message;
+            msg += "</div>";
+
+            msg += " <div class=\"noVNC_location\">";
+            msg += event.filename;
+            msg += ":" + event.lineno + ":" + event.colno;
+            msg += "</div>";
+
+            if ((event.error !== undefined) &&
+                (event.error.stack !== undefined)) {
+                msg += "<div class=\"noVNC_stack\">";
+                msg += event.error.stack;
+                msg += "</div>";
+            }
+
             document.getElementById('noVNC_fallback_error')
                 .classList.add("noVNC_open");
-            document.getElementById('noVNC_fallback_errormsg').innerHTML =
+            document.getElementById('noVNC_fallback_errormsg').innerHTML = msg;
-                msg + '<br><br>' + 'at: ' + file + ':' + line + ':' + col;
         } catch (exc) {
             document.write("noVNC encountered an error.");
         }

vnc.html

@@ -68,6 +68,7 @@
 
     <div id="noVNC_fallback_error">
         <div>noVNC encountered an error:</div>
+        <br>
         <div id="noVNC_fallback_errormsg"></div>
     </div>