Using HyperSpec when loading a page via `visit`

If you visit a page (rather than use `mount`) you don't get the HyperSpec extra stuff (like TimeCop integration, ability to use `before_mount`, `insert_html` etc.

Furthermore, when you call on_client the @hyper_spec_mounted flag is not set, and so the page will get reloaded.

You can work around the second part by doing a `page.instance_variable_set("@hyper_spec_mounted", true)` after the visit.

But this should all be nicely integrated, possibly some ERB helpers that could be used in test mode when loading the layout?