logging alert messages
Be able to manipulate confirm boxes. (fixed #153)

thanks gongo for helping in https://gist.github.com/znz/4993414
Be able to manipulate prompt boxes.
add Changes to README.md
Merge remote-tracking branch 'znz/manipulate_dialog_boxes'

Conflicts:
	README.md
	lib/capybara/poltergeist/browser.rb
	lib/capybara/poltergeist/client/browser.coffee
	lib/capybara/poltergeist/client/compiled/main.js
	lib/capybara/poltergeist/driver.rb