Archiving workunit appear to be losing helper files (e.g. cpp's) sometimes.

I have not managed to reproduce it, but have seen several workunits in Dataland whose helper cpp files were not archived, and so were missing on restore.

On other workunits that I had not yet tried to restore, I confirmed the were missing in the sasha archive location.

Examples in dataland:
W20160720-152629
W20160718-154503-7
W20160718-141503-2

I tried manually archiving (with cmdline sasha action=archive) but could not reproduce the issue.