protect javascript from invalid mime-type data

everything is a string, if anything else is sent,
drop it so it doesn't show up in the notebook document.

IPython/html/static/notebook/js/outputarea.js

@@ -277,11 +277,26 b' var IPython = (function (IPython) {'
         "javascript" : "application/javascript",
     };
 
+    OutputArea.prototype._safe_set_mime = function (src, dest, srckey, destkey) {
+        destkey = destkey || srckey;
+        
+        var value = src[srckey];
+        if (value !== undefined) {
+            // For now, everything is a string,
+            // but JSON should really not be double-serialized.
+            if (typeof value !== 'string') {
+                console.log("Invalid type for " + destkey, value);
+            } else {
+                dest[destkey] = value;
+            }
+        }
+    };
+
     OutputArea.prototype.rename_keys = function (data, key_map) {
         var remapped = {};
         for (var key in data) {
             var new_key = key_map[key] || key;
-            remapped[new_key] = data[key];
+            this._safe_set_mime(data, remapped, key, new_key);
         }
         return remapped;
     };