Fixes Z-shift observed bug where vwf.getNode() could falsely trigger the creation of additional nav objects, #2671.

Added a flag to the threejs view driver getProperty('userObject') & gotProperty('userObject') to prevent false triggers with outstanding getProperty calls.  

The z-shift test case can potentially go away.  Used to reproduce the unique situation.

FYI: Added another redmine issue for implementing a callback for get/got property.  #2812.  This fix will probably go away once 2812 is resolved.