Avoid cloning volumes more than once for the same node in alignment (saves memory). Added reference counting for volumes - for now just counting how many instances the volume has in nodes. Fixed node bits which were overwriting TObject bits space. Do not allow setting max threads if geometry not closed. Removed assigning dummy media to assemblies. Improved debugging info for assemblies.
(cherry picked from commit c28027389dbc6e4bd713e4fb389f5ea35b77d7f7)

Conflicts:

	geom/geom/src/TGeoPhysicalNode.cxx
Fixed warnings