Hall A Analyzer

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.