70 x hcal pre mix bugfix

Modifications for Hcal PreMixing.  Technically, digitization is not done; the scaled fC values are passed directly and reconstituted.  This removes any digitization noise.  Overflows are handled by setting the error bit on that sample (note bugfix to the HcalPacker to allow this!) and then using the "standard" adc->fC conversion for these values.