Fix {{#with view.foo as bar}}

The `with` helper can correctly bind through the `view` keyword when
it's used like this:

    {{#with view.foo}}

But the binding is broken if you try it like this:

    {{#with view.foo as bar}}

This change fixes it.
Merge pull request #5115 from ef4/with-keyword-as

Fix {{#with view.foo as bar}}