Only stop if the transition on this element ended

This way it doesn't end when some random element elsewhere on the page has an ending transition.

It must be noted that this is not a complete fix. If you have multiple transitions on the element, it still ends when the first ends.

I ran into this not working (the transition ends almost immediately, because some unrelated transition ends). This fixes it for me, but I was wondering whether this cornercase was considered, and whether the other cornercase (multiple transitions) was considered.

I think it's very hard to get this correct, and think it might be better to make the timeout explicit, or at least allow to set it explicit, and fall back to this behaviour. But I'm really interested in feedback on this one.
Guard against contentEditable with children props
Added event parameter
Make sure it works when we have no css transitions
add picture element and related attributes
add picture to xjs.knownTags
Add support for <dialog> tag.

fixes #2017
Add 2048-react to open-source demos

Nothing too complicated, but I think it could be a fun beginner demo.
use attribute for media, srcSet and sizes
Docs: renamed input's state to `message`

Readers might feel confused with the actual input's `value` attribute.
Fix typo
Improve debugging for methods using ReactPerf
Combine displayName using underscore
Add newline before JSX spread when appropriate

Previously, we were losing the newline before a JSX spread attribute which would cause the lines to not match up; this fixes the problem.
Include vendor/ when running jest tests

Now the two transform tests get run alongside the React core tests.

Test Plan: jest
Enable ES7 spread transform when using --harmony

Test Plan: `echo "var o = {...x};" | bin/jsx --harmony` outputs `var o = Object.assign({},x);`.
Merge pull request #2118 from spicyj/es7-spread

Enable ES7 spread transform when using --harmony
Merge pull request #2117 from spicyj/jest-vendor

Include vendor/ when running jest tests
added production example

Addition note: Scribbler.co uses an infinite.js/UITableView like rendering pattern with animations which is only possible because of React.
SVG logo

I traced the current logo in Illustrator to get a good version. And with
SVG we don't need any 2x magic because it's already vector. I should
probably care about IE8, but I don't.