throw error when setState's arguments are bad
better error message for mergeHelpers and setState
Don't store mount image on component instance
CSS widows property is unitless

Ref #836
More unitless CSS properties

volume, stress, pitch-range, richness
Refactor unit test
Unitless CSS flex properties
CSS column-count property is unitless
Improve "Can only mount when umounted" message
"checkbox" not "checked"

I can only assume this was a typo.
Merge pull request #878 from spicyj/mount-unmounted

Improve "Can only mount when umounted" message
Add dataType to all $.ajax calls for consistency

Fixes https://groups.google.com/forum/#!topic/reactjs/WWA3ZqU6y4w.
Remove unnecessary 'NA'-fallback for getTextContentAccessor()
Allow null return values for functions to-be-merged.
Update docs to mention that you need both es5-shim.js and es5-sham.js to use React with IE8.
Fix typo in docs.
Make findComponentRoot faster with more nodeCache

This is an alternative, less-invasive, fix for #891.

Test Plan:
On http://jsbin.com/OqOJidIQ/2/edit, got timings like

[75, 56, 30, 36, 27, 27, 28, 32, 27, 27, 28, 31]

instead of the old

[75, 729, 46, 32, 28, 34, 26, 27, 27, 30, 26, 26].

I also added a counter to getID and saw it was called 3014 times instead of the old 636264. (3014 is the number of nodes (3000) plus 3 calls that happen for the initial render and 1 for each of the 11 renders after that.)
Merge pull request #884 from spicyj/tut-datatype

Add dataType to all $.ajax calls for consistency
Merge pull request #895 from spicyj/zomgperf

Make findComponentRoot faster with more nodeCache
Wrap _performComponentUpdate call in try/finally

Fixes #208. If you attempt a state update with a bad state then the render will fail (and the DOM won't change) but if you switch back to a valid state later then it'll rerender properly.