Do not create range with default document.

[davireis]

Hi,

I stumbled upon this while using findText within an iframe, which happens in my mocha+phantomjs test setup. This is the error message:

  1) ...:
     Error: WRONG_DOCUMENT_ERR: DOM Exception 4
      at http://localhost:9000/app/bower_components/rangy/rangy-core.js:2304
      at updateNativeRange (http://localhost:9000/app/bower_components/rangy/rangy-core.js:2228)
      at http://localhost:9000/app/bower_components/rangy/rangy-core.js:1969
      at http://localhost:9000/app/bower_components/rangy/rangy-core.js:2360
      at http://localhost:9000/app/bower_components/rangy/rangy-textrange.js:1714
      at http://localhost:9000/app/bower_components/rangy/rangy-textrange.js:1514