use resize instead of reserve


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48558 27541ba8-7e3a-0410-8455-c3a389f83636
from Max Baak: use %e instead of %f. 
The command is written out as a string, and %f is only 6 digits long, the bug is that HistFactory 
screws up the normalization of RooRealSumPdf when the value of (1/bin width) becomes too small,
e.g. as would happen for a bin of a >100 GeV, in units of MeV.


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48559 27541ba8-7e3a-0410-8455-c3a389f83636