remove references to react-page
Fix animation example code

key should never be index into an array or there are bugs. Especially in
transitions.

Fixes #853
Use querySelectorAll instead of getElementsByName in ReactDOMInput.

We've been able to use `querySelectorAll` in all the browsers that we
support for some time now, but we haven't been able to test code that uses
it in the older version of `jsdom` that we were using, until recently.

Besides the general goal of modernizing our code, the impetus for this
specific change is that I'm trying to support testing without having to
render nodes into an actual document. The `.getElementsByName` method is
only defined on `document` and only works if the nodes you care about are
contained by the document.

On the other hand, `querySelectorAll` works on any DOM node, and allows a
more precise selection of just the `<input type="radio">` elements that
have the appropriate name.

IE8's implementation of `querySelectorAll` supports attribute-based
selectors, which is all we need here.
Warn for numeric object properties

Numeric keys will be ordered sequentially in Chrome/Firefox.

Warn the user if such keys are set on a child.
fix grammar mistake
Support `children` and `ref` for `cloneWithProps()`

We're not handling these correctly.
Fix warning for numeric properties

Number('.1') === 0.1, and react uses dot-prefixed keys
for children. Whoops. Nuke the non-numeric requirement, and just
check a regex. This seems performant enough in micro-benchmarks:
http://jsperf.com/numericlike
Add documentation about React.renderComponent

Recently learned that components passed into `React.renderComponent` may not be the ones actually mounted. Also learned that it returns the mounted component. Added some documentation describing this.
s/Mock DOM/Virtual DOM/

Let's be consistent with the naming