Mustache {{#if}} does not correctly evaluate boolean value

[foxdonut]

Please refer to:
http://jsfiddle.net/foxdonut/AUZmf/

{{hasDucks}} evaluates to false, but {{#if}} considers it true, displaying "Ducks:". Instead, it should display "No ducks!"

[bmomberger-reciprocity]

It works if you make it a can.compute.

http://jsfiddle.net/AUZmf/10/

This relates to the fix I made for #292. I only considered computes and not other functions. A non-compute function is treated as a static value when it's an argument to a helper, and function objects are truthy.

[andykant]

Added Mustache.resolve that'll resolve any variable the same way it would normally be interpolated and updated the default helpers to use this for evaluating truthyness.