Refactor OperatorMsg.chpl and BinOp.chpl

[1RyanK]

It might be good to refactor the procs so that rather than conditioning on types inside e.g. doBinOpvv, there's a where in the function signature that brings calls directly to the correct proc implementing that case. Furthermore, there's a lot of overlap between the actual operator handing; could there just be a few procs that do something like

      select op {
        when Mul { e = (l.a: etype * r.a: etype): etype; }
        when Add { e = (l.a: etype + r.a: etype): etype; }
        when Sub { e = (l.a: etype - r.a: etype): etype; }
        when Div { e = (l.a: etype / r.a: etype): etype; }
        when Mod {
          ref ea = e;
          ref la = l.a;
          ref ra = r.a;
          [(ei,li,ri) in zip(ea,la,ra)] ei = modHelper(li: etype, ri: etype): etype;
        }
        when FloorDiv {
          ref ea = e;
          ref la = l.a;
          ref ra = r.a;
          ea = floorDivision(la, ra, etype);
        }
        when Pow {
          e = ((l.a: etype) ** (r.a: etype)): etype;
        }
        otherwise do return MsgTuple.error(nie);
      }

and handle this for multiple functions?