make ReactTransitionChildMapping or flattenChildren public API

[jedwards1211]

I just created a PR for an issue with ReactTransitionGroup: jedwards1211#1

I was able to use this with 0.13 for a long time by using my own fork of ReactTransitionGroup, which of course relies on

var ReactTransitionChildMapping = require("react/lib/ReactTransitionChildMapping"); 

But it looks like in 0.14 this kind of approach will no longer be possible, and flattenChildren is deeply intertwined with a lot of React internals.

If it were possible to use the same internals that ReactTransitionGroup does, people could create innovative new components. For example, I have long wanted to create a variation that automatically staggers child entry, even if children are all added at the same time, for the classic staggered animation effect. That would be quite useful, no?

[sophiebits]

I think you can use React.Children.toArray now and key off of the resulting .key properties to build your own map.

[jedwards1211]

@spicyj Ah, okay, thanks!