Add functions for cut statistics to THaFormula
For special applications, it might be interesting to add two functions to
THaFormula that evaluate to statistics of
THaCuts: number of times called and number of times passed. Hall C's
hcana currently implements a version of this in
THcFormula for end-of-run reports.
It would be cleaner to merge the Hall C features directly in the
THaFormula base class. This can be done pretty easily, for example, by using the "index" field of
THaFormula::FVarDef_t to values other than zero. If
FVarDef_t::type == kCut, then
FVarDef_t::index indicates the evaluation mode: 0 = current result, 1 = number of times called, 2 = number of times passed.