Especially from borg, where the content identifier logs
all end up being the same identical file!
But also, for other imports, the location tracking logs can,
in some cases, be identical files.
Bonus optimisation: Avoid looking up (and parsing when set)
GIT_ANNEX_VECTOR_CLOCK env var every time a log is written to.
Although the lookup does happen at startup even when no
log will be written now.
For reasons explained in the bug report.
Implemented using a persistent migration, which works fine. It may add a
little startup overhead when a remote is enabled that uses this, but
probably un-noticable.
On the next major version, it would be fine to delete this database,
and regenerate it from the git-annex branch information. Then this
change could be reverted.
Did nothing about adding back the data that got dropped from the db
due to the bug. Only the borg special remote was probably affected,
and it's not been released yet. rm -rf .git/annex/cidsdb does work.
Note that, after changing it with enableremote, syncing won't rescan
known archives in the borg repo using the changed config. Probably not a
problem?
Also used File in some places where filenames that could theoretically
start with - are passed to borg, to avoid it confusing them with
options.
Don't want to try to use these remotes as key/value remotes, which will
surely fail. It only recently became possible for importtree to be set
w/o exporttree, so before this code was ok.
(cherry picked from commit 97599cb0f7f4115aa5a3e81a91ee3d1d6c52dc84)
