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] Update Flux TodoMVC Tutorial
[docs] fix nits
[docs] remove redundant paragraph
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
Merge pull request #2080 from fisherwebdev/master

[docs] Update Flux TodoMVC Tutorial
Fix console warning in LegacyImmutableObject

It does check `hasOwnProperty`, but *after* accessing the field and therefore triggering enumerable getters in modified prototypes.
Add version to legacy factory monitoring
Don't transfer props to mocked empty component

We currently automatically render empty components in place of mocks. However,
we were accidentally transferring the props from the mocked descriptor to the
empty component placeholder. Even children.

This change just cleans that up and should only affect unit tests.