When adding a new version of a file, and annex.genmetadata is enabled,
don't copy the data metadata from the old version of the file, instead use
the mtime of the file. Rationalle being that the user has requested to
generate metadata and so would expect to get the new mtime into metadata.
Also, avoid warning about copying metadata when all the old metadata is
date metadata. Which was rather the harder part.
This commit was sponsored by Boyd Stephen Smith Jr. on Patreon.
ef389722ae