nnfit does not handle write failures

Created by: Zaharid

As far as I can tell, something like this:

  ofstream fitinfo(fitfilename.str().c_str());
    fitinfo << fNIte <<"  " << erf_val <<"  "<<erf_trn<<"  "<<chi2<<"  ";
  if (posVeto)
    fitinfo << "POS_VETO"<<endl;
  else
    fitinfo << "POS_PASS"<<endl;

does nothing if there is a write failure other than set a status byte:

root [0] ofstream full("/dev/full")
(std::ofstream &) @0x7fb56f9e4020
root [1] full << "BAD WRITE";
# NOTE flush is important, otherwise we don't get any status
root [7] full.flush()
root [9] full.good()
(bool) false

I think we should handle these things somehow, by e.g. using this exception mechanism:

http://www.cplusplus.com/reference/ios/ios/exceptions/