Future proof cwp, remove unused internal utils

Adds a version check to cwp so that it only wraps `child.type` in a mock
factory for version 0.12, as it would break in 0.13, where
`react.createElement ===
require("react/lib/ReactElement").createElement` will be `true`
Merge pull request #277 from jquense/clone-with-props

Future proof cloneWithProps a little. Remove unused internal utils