adding a shallow equals assert

So I like the AssertDeepEqual. However sometimes it is nice to compare int64 to int without having to coerce the expected types, for example:

<pre>
<code>
  //Fails with (expected) 100 != 100 (actual)
  t.AssertDeepEqual(100, int64(100))
  //Works with standard equality
  t.AssertEqual(100, int64(100))
</code>
</pre>

Open to inverting the naming scheme however I think AssertEqual being shallow is the least surprising thing for folks coming from other testing frameworks.