Move heading anchors 50px up to avoid nav bar

Fixes #447.

We do this by moving the actual anchored element up in the page without moving the actual text. (Apple uses a similar trick in their framed docs.) Now this looks a bit sillier on smaller screens but it's better overall.
Fix unmounting components mounted into doc element

If we are to unmount a component mounted into a document element we should
unmount it from document.documentElement and not from document.firstChild which
is a doctype element in this specific case.
Merge pull request #423 from andreypopp/master

Re-rendering components into a document leaks components
Make 'disabled' MUST_USE_ATTRIBUTE for compatibility with CSS [disabled] selectors.

When a ReactDOMComponent is created with the property `disabled: true` subsequently setting the property to `disabled: false` the HTML attribute `disabled="true"` was being left in the DOM.
Update everything for v0.5.1

Cherry-picked from f3db0006e832e24649278c9e9eab6b9ca2c80336, excluding
version changes.
blog post for 0.5.1
Forward Compatibility w/ WebKit & Blink

Newer versions of WebKit and Blink will support both `document.body.scrollTop` and `document.documentElement.scrollTop`. Therefore, implementing cross-browser compatibility by summing the two will no longer work.

This changes React to use `getUnboundedScrollPosition` so we get the fix and consistency in one change!

See: https://rniwa.com/2013-10-29/web-compatibility-story-of-scrolltop-and-scrollleft/
Add autoCorrect to list of supported DOM properties
Reorder DefaultDOMPropertyConfig

`autoCorrect` belongs with the non-standard properties list.
Bump populist version to v0.1.4.

The new version includes a fix for this IE8 issue reported by
@subtleGradient: https://github.com/benjamn/populist/issues/4

Closes #456.
Merge pull request #457 from benjamn/upgrade-populist

Bump populist version to v0.1.4
remove examples/wrapup

Apparently it's no longer relevant.
Switch utility function calls -> namespaced calls
Better `getUnboundedScrollPosition` for windows

Instead of using browser sniffing, `getUnboundedScrollPosition` can do
better and not have to depend on the `getDocumentScrollElement` module.
[docs] Clarify when `getInitialState` is called.
Clear error message when rendering a nonvalid component
Merge pull request #465 from matnel/bug388

Clear error message when rendering a nonvalid component
remove examples/wrapup

Apparently it's no longer relevant.
Merge branch 'rm-wrapup' of github.com:chenglou/react into rm-wrapup

Conflicts:
	package.json
Fix ReactDOMSelection for IE 11

IE 11 no longer supports the legacy document.selection API.
Their implementation of window.getSelection() doesn't support
the extend() method, which we were relying on.

If the selection is RTL and selection extend is missing, then just
flip the selection.