DiffractionFocussing2 masking check for pixelIDs

[Vickie Lynch]

The TOF bins are different for the PreserveEvents option true/false at the end of SNSPowderReduction. It is the same problem fixed in Sept. 2011. See ​https://github.com/mantidproject/mantid/commit/30954f4f265442160b435f432583ae6150fade5c#Code/Mantid/Framework/Algorithms/src/DiffractionFocussing2.cpp

With the optimization of DiffractionFoccussing2 the coding to not include masked pixelIDs in the resulting spectrum has been deleted for PreserveEvents=true. When binning in dSpace and then converting to TOF for the GSAS output this changes the TOF.

This is not an urgent issue in practice. The characterization file that people are using defines what the focus position is so converting back to TOF is done to the same place with and without preserving events. The error should still be fixed, but we don't have to push to get the change out the door.

As a small point of optimization, the faster way to check for masking is found on line 602 of ​https://github.com/mantidproject/mantid/blob/master/Code/Mantid/Framework/Algorithms/src/DiffractionFocussing2.cpp.

[Vickie Lynch]

Refs #5005 added one missing line for execEvent with 1 group

Changeset: 43a9722735f8f47346514edf25ef58e64ea207de

[Vickie Lynch]

Run DiffractionFocussing2 with/without PreserveEvents and compare results after converting to TOF to test.

[Stuart Campbell]

This ticket has been transferred to github issue ​5851