- added .sha1() to n-cube.  This is in preparation for optimistic locking.  Whenever an n-cube is saved, the sha1 will be calculated and stored with it.  Before an n-cube is updated, the stored sha1 will be checked against the inboud sha1 (retrieved when loaded) to determine if the persisted n-cube changed while it was being edited.   This is very much like CVS, Git, etc and eliminates the need to actively locking and unlocking n-cubes.