Stabilize minimal server rendering API

This is a pretty killer feature and the API is simple. I know it's another API method on React, but I think it's
the only way.
Fix typechecks for isRenderedByReact()
Reduce `ReactInstanceHandles` API Surface Area

Change `ReactInstanceHandles` so that `getFirstCommonAncestorID` and `nextDescendantID` are now private (and documented to be only exposed for unit testing). Also:

 - Renamed `nextDescendantID` to `getNextDescendantID`.
 - Renamed `parentID` to `getParentID`.

I also organized `ReactInstanceHandles-test` by method names.

Functionally, this diff should not change anything.
Use `isAncestorIDOf` in `ReactInstanceHandles`

This is both a functional fix and performance fix for `ReactInstanceHandles`.

 - `getFirstReactDOM` uses `indexOf` but should be checking ancestry (via `isMarker()`).
 - Added `isAncestorIDOf`, checking ancestry can be way faster than getting a common ancestor: http://jsperf.com/react-ancestor-id-check
Rename "Delegate" to "Synthetic"

This is just a simple rename of the event classes to `SyntheticEvent`. I've also updated the constructor arguments to be more correct:

 - `dispatchConfig`: Data used by the plugin system for dispatching the event, for example: `{registrationName: 'onClick'}`
 - `dispatchMarker`: An identifying marker used to describe where the event is occuring, for example: `.reactRoot[0]`
Fix Event Normalization in IE<9

IE<9 relied on the `target` property being overriden. This adds back a hack that only applies in IE<9. I'll be able to revert this hack once I check in synthetic events.
Add missing license headers