WIP: Support for capybara 2.3

I'm going to implement the support for capybara 2.3, keep the pull request open until it's finished :)
@yaauie capybara does not accept to call visit with a space on path anymore, it raises an bad uri exception.

I think what poltergeist is supporting was a undocumented feature that was causing trouble to cookies, see [this commit](https://github.com/teampoltergeist/poltergeist/commit/e2eb7c38b317e56e4008603d74adcb6afd8e4146) and [this one](https://github.com/jnicklas/capybara/commit/bb942e94d3c0731526b0f4b7d3c9b054755ea288).

It may be considered a regression of capybara but it wasn't supposed to work.

We can fix it on capybara and make a conditional to run this scenario, wdyt?