Issue #329, special check for the common and magical 'length' property.

underscore.js

@@ -675,6 +675,8 @@
     }
     // Ensure that both values are objects.
     if (typeA != 'object') return false;
+    // Arrays or Arraylikes with different lengths are not equal.
+    if (a.length !== b.length) return false;
     // Objects with different constructors are not equal.
     if (a.constructor !== b.constructor) return false;
     // Assume equality for cyclic structures. The algorithm for detecting cyclic structures is