Fix _.isEquals() for wrapped objects

This caught me out when writing some unit tests that use _.isEquals().
They were all passing even though I knew they shouldn't be, and I
realised I was checking equality with a wrapped object that I'd
forgotten to unwrap.

underscore.js

@@ -519,6 +519,9 @@
 
   // Perform a deep comparison to check if two objects are equal.
   _.isEqual = function(a, b) {
+    // Unwrap any wrapped objects
+    if (a && a._chain) a = a.value();
+    if (b && b._chain) b = b.value();
     // Check object identity.
     if (a === b) return true;
     // Different types?