Fix IE incompatibility

Handlebars now aliases toString as Object.prototype.toString, but
due to the way we wrap the individual parts of Handlebars, when
executing isEmpty IE will use the window scope for toString. This
makes the reference explicit.
Merge pull request #92 from drd/handlebars-1.0rc3

Fix IE incompatibility
handleabar -> Handlebar
Merge pull request #94 from salami162/master

handlebar -> Handlebar