Warn if a goog.scope alias uses a different name from the last part of the original name

When creating a short alias for `some.really.long.name.Foo` the alias should almost certainly be `Foo`. If someone writes

``` js
goog.scope(function() {
var Bar = some.really.long.name.Foo;
});
```

it is surprising and a violation of the style guide. We could probably warn for this pretty easily in the [ScopedAliases pass](https://github.com/google/closure-compiler/blob/master/src/com/google/javascript/jscomp/ScopedAliases.java)