[whatwg] Fixing undo on the Web - UndoManager and Transaction

[Ryosuke Niwa]

Hi all,

I've updated the working draft: http://rniwa.com/editing/undomanager.html

The summary of changes:

   - Managed transaction has been renamed to automatic transaction
   - Moved undoManager IDL attribute from Node to Element and Document
   - Automatic transactions no longer undo/redo DOM changes outside of the
   undo scope
   - Recursively applying, unapplying, or reapplying transactions on the
   same undo manager is now forbidden
   - Removed host attribute from Transaction interface
   - Added transaction events and TransactionEvent interface

- Ryosuke