Riccardo's fix to physical volume proliferation is now working across Ubuntu and Mac platforms.

This MR re-activates a bugfix to the problem that multiple copies of physical volumes are created when reading in a .db file. It also implements a bugfix to the bugfix that first surfaced on Ubuntu platforms during restore operations, although it was due to a problem in saving the .db file.

Now geometries which are restored from an SQLite file have the same physical volume tree as when they were saved.

However, we need further work to assure that shared instances of IdTags,, Transforms, Alignable Transforms, and NameTags be shared after a save/restore cycle. In all of ATLAS, this fails to occur at the level of only a very few instances.