#13 Properly report errors with labelit indexing

[Graeme Winter]

I.e. when an image has too few reflections. Report problem, recommend use of different command-line options? Or -failover to something smarter?

Internal trac # 1341.

[Graeme Winter]

bcsb-nx 20% cat .../XIA2_OUTPUT/DEFAULT/NATIVE/SWEEP1/index/2_labelit.index.log
.../LINK_TO_IMAGES/test_1_001.img
.../LINK_TO_IMAGES/test_1_045.img
.../LINK_TO_IMAGES/test_1_090.img
Spotfinder Problem: Too few unimodal Bragg spots (33) in image 1
The minimum allowable number of Bragg spots per image is set to 40.
Override this by creating a file "dataset_preferences.py" file with, e.g.:
distl_minimum_number_spots_for_indexing = 33