Merge pull request #4971 from syuvivida/72x_20140815_weight

Codes require to save generator cross section in each luminosity block
Merge pull request #5601 from syuvivida/73x_fixXSec_eiko

GeneratorInterface -- Codes that fix the cross section computation
improve printout in GenXSecAnalyzer and add to default filter summary sequence
add missing dictionary for GenLumiInfoProduct data member
skip cross-section calculation if GenLumiInfo is not available (eg for single particle gun)
Merge pull request #5617 from bendavid/xsecbackport_53x

Backport of GenLumiInfoProduct and associated cross section machinery to 53x