StiIstDetectorBuilder: Added flag to build ideal IST geoemtry
StiIstDetectorBuilder: We need to set the current gGeometry path before extracting any info about current volume position
StiIstDetectorBuilder: Yaping's changes
Merge branch 'ds-ist'
Updated in accordance with the nee pileup trees stucture.
Updated the instructions.
StiDetectorBuilder: Added a method to save Sti geometry into a root file. The conversion to drawable objects is done by means of StiMaker/StiDetectorVolume class
StiXXXDetectorBuilder: Save Sti detector geometries as drawable objects in root files when 'debug2' option is specified in BFC chain