Clean up compile warnings

[hschellman]

There are a bunch - I've found unused-value and overloaded virtual to be the most common.

OSX complains a lot about HistFolio

/Users/schellma/MAT3/opt/lib/../include/PlotUtils/HistFolio.cxx:176:11: warning: expression result unused [-Wunused-value]
assert(("ERROR: hist map and array size mismatch",
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

boatloads of
/Users/schellma/MAT3/MAT/PlotUtils/MnvVertErrorBand.h:64:18: warning: 'PlotUtils::MnvVertErrorBand::Fill' hides overloaded virtual functions [-Woverloaded-virtual]
virtual bool Fill( const double val, const double *weights, const double cvweight = 1., double cvWeightFromMe = 1.);
^
/Users/schellma/miniconda/envs/ccqe/include/TH1.h:219:21: note: hidden overloaded virtual function 'TH1::Fill' declared here: different number of parameters (1 vs 4)
virtual Int_t Fill(Double_t x);
^
/Us
Maybe those can be hidden with -Wno-overloaded-virtual/ Although I can't seem to make that work. I still get complaints. Is -Wall going first overriding it?