For now, it's only allowed when exporttree=yes is also set.
That simplified the implementation, but could later be changed if
there's a remote that makes sense to be an import but not an export.
However, it may work just as well to make a remote be readonly to
prevent export to it while still allowing import.
This does not avoid all possible races, but it does avoid all likely
ones, and is demonstratably better than git's own handling of races
where files get modified at the same time as it's updating the working
tree.
The main thing this won't detect are not unlikely races where part
of a file gets changed while it's being copied and then the file is
restored to its original condition before the modification check.
No, it's more likely that the limitations of checking inode, size,
and mtime won't detect certian modifications, involving eg mmapped
files.
Made some api changes.
listImportableContents needs to provide the size
of the data, so the downloader can check disk free space.
retrieveExportWithContentIdentifier is passed the filepath to write to
Use temporary "CID" key during download of a ContentIdentifier from a
remote, so withTmp can be used and then move the content to the real key
once it's known.
Added graftTree but it's buggy.
Should use graftTree in Annex.Branch.graftTreeish; it will be faster
than the current implementation there.
Started Annex.Import, but untested and it doesn't yet handle tree
grafting.
