fsfs hotcopy should copy live locks/ consistently

Philip notes that FSFS hotcopy duplicates the locks/ dir by doing a simple recursive copy, and that doing so may cause the duplicate to be inconsistent if the locks/ dir is live (locks are being added or removed) while the recursive copy is running.

(If a deep child was locked, the duplicate might contain have directories that refer to that child even though those directories' parents don't refer to it.)

Current proposed solution:
email from Daniel Shahaf to dev@, 2010-11-13, "Re: FSFS locks questions and a concern", archived at haxx.se gmane.org

Some prepare-the-ground work was done:
r1034040

A proposed patch:
email from Daniel Shahaf to dev@, 2010-11-13, "Re: FSFS locks questions and a concern", archived at haxx.se gmane.org