Fix bug with root path that causes ember query-params support to break.

The rootPath property is built from the current url. When there are query params it would cause a malformed resource URL to be generated. e.g. http://emberjs.com/api/v1?page=1/articles.json
Merge pull request #42 from endlessinc/ember-query-params

Fix bug with root path that causes ember query-params support to break.