some changes in the class TGeoPNEntry (needed for alignment purposes):

1. Constructor of TGeoPNEntry performs a check upon definition of a symbolic link to a physical node. The check is done redundantly also upon creation of a physical node starting from a symbolic link to prevent mis-usage of these objects in-between geometries.
2. Allows storage of an additional user-defined TGeoHMatrix. The matrix should be created by the user but
once TGeoPNEntry::SetMatrix() is called becomes owned by TGeoManager.


git-svn-id: http://root.cern.ch/svn/root/trunk@16298 27541ba8-7e3a-0410-8455-c3a389f83636