Provide errors for failed async props

[jdolle]

I propose to wrap component render function to provide props as the first argument and errors as the second.

Wrap SFCs to do the same.

By solving the problem like this, the method of rendering components is unified. No more this.props.

However, by solving it this way we also add a little "magic" on top of React. An alternative might be to provide this.errors for components.