improve test by adding a test for normalized scaling via TH1::Add for variable bin histograms

(the test works after r42299 fix in TH1::Add)

Fix also comparison of entries/effective entries for THnsparse which made the projection tets failed after 
r42189


git-svn-id: http://root.cern.ch/svn/root/trunk@42300 27541ba8-7e3a-0410-8455-c3a389f83636