Monkey-patch urllib3 with PyOpenSSL-backed SSL-support.

def inject_into_urllib3():
    'Monkey-patch urllib3 with PyOpenSSL-backed SSL-support.'

    _validate_dependencies_met()

    util.ssl_.SSLContext = PyOpenSSLContext
    util.HAS_SNI = HAS_SNI
    util.ssl_.HAS_SNI = HAS_SNI
    util.IS_PYOPENSSL = True
    util.ssl_.IS_PYOPENSSL = True