Add a method to the js sdk to look up 3pids on the ID server.

lib/http-api.js

@@ -245,7 +245,12 @@ module.exports.MatrixHttpApi.prototype = {
             opts,
             requestCallback(defer, callback, this.opts.onlyData)
         );
-        return defer.promise;
+        // ID server does not always take JSON, so we can't use requests' 'json'
+        // option as we do with the home server, but it does return JSON, so
+        // parse it manually
+        return defer.promise.then(function(response) {
+            return JSON.parse(response);
+        });
     },
 
     /**