Fixes within_frame for Cross Domain Frames

As per #183 but with a working spec and a better fix
Add Capybara 2 compatibility
Merge pull request #211 from errm/master

Fix within_frame with cross domain frames
Add changelog for previous commit
We're doing injectAgent() before every evaluate now

So we don't need it in other places.
Merge remote-tracking branch 'brutuscat/master'

Conflicts:
	README.md
Remove 1.8 rubies from .travis.yml

We're on Capybara 2 now, which doesn't support Ruby 1.8
We're ruby 1.9 only now
OS X font crashes have been fixed, remove from README
spec helper tidying
Fix `within_frame` not switching context back properly

Closes #242
adding a failing test for iframe click
Fix calculation of click position when inside a frame

Closes #222, #225
Remove childprocess dependency

We no longer need to support Ruby 1.8.
Remove multi_json dependency

Since we depend on Ruby 1.9, we can rely on the presence of json in the
stdlib.
return nil if no expires on cookie (fixes #203)
Merge pull request #243 from arnvald/expires_nil_by_default

return nil if no expires on cookie (fixes #203)
Slight refactor
Fix the :js_errors => false option

Closes #229
An error inside PoltergeistAgent should be a BrowserError

Previously we raised a JavascriptError, which is for the user's own
Javascript on the page.