addSubFile with auto-commit feature
addSubFile with auto-commit feature

Following removeSubFile, addSubFile also has auto-commit
feature, paving the was to refactor swapSubFiles and PromoteSuperFile.

afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform,afishbeck/HPCC-Platform