COUndoTrack: switch to applying commands using COStoreTransaction, so a large number of undos can be committed in a single store transaction. Undoing 10 or 20 undo commands at once in Typewriter is nearly instantaneous now (for some reason, redoing is slower; need to investigate). 

There is also a hack here in COSQLiteStore, which is that -commitStoreTransaction: now waits for the notification it posts to be processed before returning. This allows COUndoTrack to call -commitStoreTransaction:, and when the call returns, any editing contexts in the same process will have already processed the changes (so COUndoTrack behaviour is the same as before, when it used to use -[COEditingContext commit] to save changes)

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/CoreObject@10336 7b3f36aa-e6db-49c1-8b4c-66eac1997e64