Improve EllipsoidGeometryUpdater performance

The fast path for dynamic ellipsoids in the DataSource layer was not
checking the value of instance attributes before setting them, leading to
a large slowdown in performance.  With 170 time-dynamic ellipsoids,
this went from 15 fps to 100.
Merge pull request #2320 from AnalyticalGraphicsInc/dynamic-ellipsoid-performance

Improve EllipsoidGeometryUpdater performance