update the TrackerMaterialAnalysis package to CMSSW_6_2_X

 * merge CMSSW_6_2_X_SLHC fixes into CMSSW_6_2_X
 * revert and reimplement 7a4840c0d5eb32e3dc68ed695e6db6ea8f39c82a
 * add preliminary support for multiple IOVs
 * move per-layer plots to a subdirectory