getChildContext() should only return its own props

i.e the ones defined in the propTypes (typesSpec here)
Merge pull request #16 from juandopazo/sauce

Add browser smoke tests in Saucelabs
Merge branch 'master' of github.com:athibaud/react-intl into athibaud-master
Merge branch 'athibaud-master'
Simplify getChildContext