ISIS-865: checks if any (non-Command) objects have been dirtied in an xactn initiated by an action with safe-semantics; if so, and if "isis.persistor.ensureSafeSemantics" is "true", will abort xactn.

Whichever way setting, will log with ERROR severity.

NB: this feature requires a CommandService impl that supports the new Command2 API.

Also supported in integ tests.

The default is taken to be "false", ie only log error, don't abort xactn.  This is for backward compatibility with 1.6.0 and previous versions.