Flag for clean cyclic logging files

[nseidle]

See issue here.

[PaulZC]

The fix for this is in pcUpdates. It is included in PR #701

I think it covers all the options. I was worried there would be a gotcha when (e.g.): going from length alignment enabled to disabled; going from a long file length to a shorter one. But, I've tested it, and it seems to behave well. If you do see weirdness, "4) Start new log" should cure all ills...