Allow empty strings for HTML
Fix for a memory leak in dispatchEvent()

The array in question grows with duplicate entries everytime
dispatchEvent() is called when mixing onfoo="" with
addEventListener("foo", ...)
Event phase AT_TARGET should also fire capture listeners

Fixes #855
The event phase AT_TARGET should also fire events registered with
capture=true on the event target, not just capture=false. Note that
calling stopPropagation during AT_TARGET should not prevent any listeners
registered on that same event target from being called.
eventPhase and currentTarget should be reset after dispatch

As per spec, before and after an event has been dispatched,
Event.eventPhase should be set to NONE and Event.currentTarget should be
set to null.
Avoid error document.cookie = null
Test that doc.cookie = null returns null and has no effect
Add a setter for NodeList.length

Apparently, Firefox's `Array.prototype.splice` sets `length`. This fails without
a setter, so add one that just returns the current value of `this._length`.
Make jsdom browserifiable and add browser test runner

To run the tests: `node test/browser-runner.js`. The runner accepts the same
options as `test/runner`, as well as some optional arguments that control the
test setup.