* No need to re-compile RPN token array on reference change alone.  We do that
  when the formula contains one or more names that have been updated.

* Adjust undo code to get it to work without relying on ref undo document,
  which would cause the token arrays to be unnecessarily recompiled.

* Whatever else need to be changed in order to pass all unit tests.

Change-Id: I99e86d23320aca8900fef011da23a9d34e42751e