ADDRESSES #52: options not passed on to included files.

Twig.Template.prototype.importFile didn't pass options on to the new
template object. Meaning that options like strict_variables wasn't
passed on.
And it resulted in the function Twig.expression.definitions.parse
throwing an TypeError because this.options didn't exist.

https://github.com/justjohn/twig.js/issues/52
Merge pull request #58 from m-abs/master

Twig.Template.prototype.importFile didn't pass options on to the new template object.