Simplify composite lifecycle state

We now forbid calling setState or forceUpdate if any component's render function is higher in the stack, not just the component you're trying to update. (We do this already now for React.renderComponent and React.unmountComponentAtNode.)

This also has the advantage that we can now remove CompositeLifeCycle.RECEIVING_STATE, making _compositeLifeCycleState easier to reason about (not to mention that RECEIVING_STATE was a confusing name) and making it possible to remove a try/finally from the render path which might help with perf.
Also list <form> in error message as possible culprit
Fix IE8 potentially throwing during restoreSelection
Update videos.md

Adding video for my recent talk in London about using React in large scale applications
Update videos.md

reordering to spot #4
Merge pull request #1835 from amm385/patch-1

Update videos.md
Update 2014-07-17-react-v0.11.md
Fix appearance of video thumbnail
Merge pull request #1860 from KyleAMathews/patch-3

Not a candidate anymore
fix typo

Closes #1859.
Update Todo MVC example

A small patch for the Todo MVC example to use React 0.11.0.
This then allows the `MainSection` to return `null` instead of
previous `<noscript/>`.
getModifierState is case sensitive
Merge pull request #1837 from garrensmith/update-todo-example

Update Todo MVC example
Don't initialize reconcile transaction on server

...when calling setState from within a componentWillMount. Fixes #1866.

Test Plan: jest
Merge pull request #1869 from syranide/modistatecase

getModifierState is case sensitive
Merge pull request #1870 from spicyj/gh-1866

Don't initialize reconcile transaction on server
Fix browser-tranforms
Merge pull request #1876 from petehunt/fix-jsxt2

Fix JSXTransformer
Move key/ref off props and prepare for new descriptor factories

Breaking changes

- key/ref are no longer accessible on props but they are accessible on the
  descriptors. This means that parents/owners can access it but not the
  component itself.

- Descriptor factories are now plain functions and you can't rely on the
  prototype or constructors of descriptors to identify the component type.

Existing descriptor factories are now wrapped in a legacy factory. Currently it
does nothing but it will give us a hook to track callers to factories that are
not using JSX but just invoking the function directly. It also proxies static
methods/properties to the underlying class. The newer factories don't have this
feature.

ReactTextComponent has it's own little factory because it's props is not an
object. This is a detail and will go away once ReactTextComponent no longer
needs descriptors.
Avoid leading spaces when first argument to joinClasses is falsy.

This detail is going to become more important once the idiom
`className={joinClasses(this.props.className, newClass)}` becomes more
common, as it will when we move away from `this.transferPropsTo`.