Resolve possible lambdas for partials

[leshill]

Hi @wycats,

I just ran across this today. We are using fairly complex context objects and wanted to invoke a partial with a context that was a function not a property. Let me illustrate with a completely contrived example. WIth this context:

{ first: function() { return this.data[0]}, data: [{name: 'Handlebars'}]};

And this partial invocation:

{{> partial first}}

The result for a simple partial of Name: {{name}} should be "Name: Handlebars".

This might resolve #182 and remove the need for #368

I am bummed that I missed the ember.js talk, if you are around Seattle tomorrow (Friday) I would like to buy you a coffee at Victrola on Pike (really great coffee).

[leshill]

After using this for a while, I am closing this PR. This needs to be part of a larger change to handlebars.js or else it is confusing. The same result can be achieved with a helper, so we are switching our code to using a helper.