From Andrei:
new class TGeoIterPlugin. 
This is an ABC for user plugins that need to call some arbitrary code during 
geometry hierarchy iteration. The first use case (requested in Savannah #57591)
is to dynamically change the color of volumes in selected paths, but not the 
color of the same volume in other paths. This use case is already implemented 
in TGeoPainter and an example of usage is given in the tutorials files 
$ROOTSYS/tutorials/geom/iterplugin.cxx and runplugin.C.


git-svn-id: http://root.cern.ch/svn/root/trunk@31454 27541ba8-7e3a-0410-8455-c3a389f83636