Fixed isEqual if second object has isEqual implemented and added isObject method

underscore.js

@@ -600,6 +600,7 @@
     if (b._chain) b = b._wrapped;
     // One of them implements an isEqual()?
     if (a.isEqual) return a.isEqual(b);
+    if (b.isEqual) return b.isEqual(a);
     // Check dates' integer values.
     if (_.isDate(a) && _.isDate(b)) return a.getTime() === b.getTime();
     // Both are NaN?
@@ -641,6 +642,11 @@
     return toString.call(obj) === '[object Array]';
   };
 
+  // Is a given variable an object?
+  _.isObject = function(obj) {
+    return obj === Object(obj);
+  };
+
   // Is a given variable an arguments object?
   _.isArguments = function(obj) {
     return !!(obj && hasOwnProperty.call(obj, 'callee'));