Seems to work ok. Unsure yet about the actual locking changes being
correct.
This is not the end of the story with upgrades, because it is unsafe for
this upgrade as implemented to run in a repository where an old
git-annex process is already running. The old process would use the old
locking method, and not notice files locked by the new, and this could
result in data loss. This problem will need to be dealt with before this
branch is suitable for merging.
Sponsored-by: Dartmouth College's Datalad project
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