Construct ProcessingInstructions correctly.

The ProcessingInstructions field was being constructed incorrectly.
Ranges were being specified using a comma, when the correct notation is
to use a colon. This patch amends this error, and also takes care of the
case where the start and end of the range are the same.

Refs #10004
Fix regressed test.

Refs #10004.
Fix regressed test. (For real this time)

Refs #10004
Merge remote-tracking branch 'origin/feature/10004_reflectometryreductiononeauto'