Fix npm react having wrong version dependency for envify
Don't get selection if no active element

Fixes #694.

Previously, it could be that there was an active element that was removed in between mousedown and mouseup.
Further cleanup of isEventSupported
Fix WheelEvent incorrectly inverting sign of deltaY
throw error when setState's arguments are bad
Don't mutate passed-in props, take 2
Use proper window object for iframe in enter/leave

Fixes #788.
Don't tack on EventPluginHub globally
Merge pull request #757 from spicyj/ng

Don't tack on EventPluginHub globally
Merge pull request #718 from syranide/npmenvify

Fix npm react having wrong version dependency for envify
Fix potential memory leak when unmounting

Fixes #781.
Spy on purgeID instead of unmountIDFromEnvironment
better error message for mergeHelpers and setState
Document return value of unmountComponentAtNode
Don't store mount image on component instance
Merge pull request #850 from spicyj/docs-ref-unmount

Document return value of unmountComponentAtNode
Merge pull request #640 from spicyj/immutable-props-2

Don't mutate passed-in props, take 2
Merge pull request #786 from spicyj/gh-781

Fix potential memory leak when unmounting
Add --harmony option to jsx.
Merge pull request #771 from spicyj/gh-694

Don't get selection if no active element