Fix argument name in `Router#paramsForHandler`

`Router#paramsForHandler` can be given objects as its contexts.
Merge pull request #46 from tricknotes/fix-argument-name

Fix argument name in `Router#paramsForHandler`
Fix null context errors with isActive

Needed for: https://github.com/emberjs/ember.js/issues/3180
Fix bug with bubbling an already-handled error

A bug was introduced in https://github.com/tildeio/router.js/pull/42
that caused errors to continue to bubble even when already handled.

This will fix the issue in
https://github.com/emberjs/ember.js/issues/3153

Also removed an inexplicable if statement that had no business being
there.
Added jshint