Remove trailing whitespace
Fix EnterLeaveEventPlugin Test in jsdom

This is a follow-up to #803.

In jsdom (used for internal testing), `<iframe>` does not properly create a default document. This makes the `EnterLeaveEventPlugin` tests work for jsdom, too.

Open source does not need this because it uses PhantomJS.
Fix Undefined `ownerDocument` Fatal in IE8

This fixes a JS fatal in IE8 when `topLevelTarget.ownerDocument` is sometimes undefined.
Better LinkedValueMixin Warning

Input elements of type `checkbox`, `hidden`, or `radio` can have a `value` without `onChange`. Also, if the input is `disabled`, who cares that it doesn't have an `onChange`?
Upsell dev tools

People probably don't know these exist. Add some information about React
dev mode as well as a link to the developer tools when using Chrome.
add React.PropTypes.any

add the ability for React propTypes to accept an `any` type: `someProp: React.PropTypes.any`.
This is more useful when combined with `.isRequired`, to enforce that _something_ is passed:
`someProp: React.PropTypes.any.isRequired`
Quieter devtools upsell

Check that we're not in a iframe before upselling.