Add a fix for urlbuilder when using local files

- The urlbuilder was generating URLs with an extra slash
  everytime we updated the browser URL (for the *file* protocol
  only)
- I've added a dirty fix for this that strip the initial slashes
  from the path
Add qunit unit tests
chan42.js: force close websocket

- The websocket close() method attempts to
  close clearly even when the connection may be
  unavailable. This causes some delay, e.g. when
  trying to reconnect.
- When we disconnect() we now immediatly clear the socket
  event handlers, an force call the close handler.