deepEqual() fails when testing objects with valueOf() equality #59

rkieffer@rkieffer-mbp$ pwd
/Users/rkieffer/repos/nodeunit

rkieffer@rkieffer-mbp$ node
> assert = require('./lib/assert.js')
{ AssertionError: { [Function: AssertionError] super_: { [Function: Error] captureStackTrace: [Function: captureStackTrace], stackTraceLimit: 10 } },
  fail: [Function: fail],
  ok: [Function: ok],
  equal: [Function: equal],
  notEqual: [Function: notEqual],
  deepEqual: [Function: deepEqual],
  notDeepEqual: [Function: notDeepEqual],
  strictEqual: [Function: strictEqual],
  notStrictEqual: [Function: notStrictEqual],
  throws: [Function],
  doesNotThrow: [Function],
  ifError: [Function] }
> x = {foo: {valueOf: function() {return 9;}}}
{ foo: { valueOf: [Function] } }
> y = {foo: 9}
{ foo: 9 }
> x.foo == y.foo
true
> assert.deepEqual(x, y)
AssertionError: {"foo":9} deepEqual {"foo":{}}
    at [object Context]:1:8
    at Interface.<anonymous> (repl.js:98:19)
    at Interface.emit (events.js:27:15)
    at Interface._ttyWrite (readline.js:307:12)
    at Interface.write (readline.js:145:30)
    at Stream.<anonymous> (repl.js:76:9)
    at Stream.emit (events.js:27:15)
    at Stream._onReadable (net.js:757:14)
    at IOWatcher.onReadable [as callback] (net.js:276:10)
>