Users should not see stack trace

[graeme-winter]

No description provided.

[graeme-winter]

For future reference - was getting

Insufficient reflections (14 < 250) to perform error modelling.
Traceback (most recent call last):
  File "/Users/graeme/svn/cctbx/modules/dials/algorithms/scaling/scaler.py", line 212, in perform_error_optimisation
    self.params.weighting.error_model, Ih_table
  File "/Users/graeme/svn/cctbx/modules/dials/algorithms/scaling/error_model/engine.py", line 36, in run_error_model_refinement
    model = model_class(Ih_table.blocked_data_list[0], scope)
  File "/Users/graeme/svn/cctbx/modules/dials/algorithms/scaling/error_model/error_model.py", line 365, in __init__
    Ih_table, basic_params, min_partiality
  File "/Users/graeme/svn/cctbx/modules/dials/algorithms/scaling/error_model/error_model.py", line 410, in filter_unsuitable_reflections
    min_reflections_required=cls.min_reflections_required,
  File "/Users/graeme/svn/cctbx/modules/dials/algorithms/scaling/error_model/error_model.py", line 565, in filter_unsuitable_reflections
    % (n, min_reflections_required)
ValueError: Insufficient reflections (14 < 250) to perform error modelling.

which I think is not user friendly

[graeme-winter]

Now

8 outliers have been identified. 

Insufficient reflections (14 < 250) to perform error modelling.
Components to be refined in this cycle for all datasets: scale, decay
Performing a round of scaling with a Levenberg-Marquardt minimizer.