Fix transition end detection for Android

Some Android versions have the "transition" and "animation" properties
set on element style objects despite not supporting un-prefxied animations
and transitions.  This change adds an additional sanity check to make sure
the correct event handlers are added for transition groups.
Actually fix transitioning to null

Test Plan: grunt fasttest
Update Dispatcher.js

I think Array.filter expects a boolean return value, am I correct?
Update Dispatcher.js
Update Dispatcher.js
Update Dispatcher.js
Embed video from F8

Edited in githubs inline editor. Not tested!
Revert "Move defaultProps resolution and type validation to the descriptor"

This reverts commit ff52e3df00ab7ed1375f46d81c122a614e202bb9.

Too many things broke with transferPropsTo
Merge pull request #1480 from volkanunsal/patch-1

Update Dispatcher.js
Fixed incorrect usage of github api in example

more: https://developer.github.com/v3/gists/#detailed-gist-representation
ReactTransitionGroup: Fix moving from falsey child

See http://stackoverflow.com/q/23510413/49485.

Test Plan: grunt fasttest
Small style fixup
Merge pull request #1276 from marcins/bugfix/1275-transitiongroup-android

Fix transition end detection for Android
Merge pull request #1490 from Vijar/master

Fixed incorrect usage of github api in example
Title case on videos page
Merge pull request #1486 from nbostrom/patch-1

Embed video from F8
Merge pull request #1460 from spicyj/tg2

Actually fix transitioning to null
Merge pull request #1492 from spicyj/rtg-from-false

ReactTransitionGroup: Fix moving from falsey child
Codemod mockDefaultReturnValue

The naming is super confusing.

mockReturnValue -> mockReturnValueOnce
mockDefaultReturnValue -> mockReturnValue
Codemod mockReturnValue externally

320024555cef1b826f8ba9e8bafccad8a5a118e7 didn't update the mocks module
here, just the callsites.