Files are now written to a tmp directory in the remote, and once all
chunks are written, etc, it's moved into the final place atomically.
For now, checkpresent still checks every single chunk of a file, because
the old method could leave partially transferred files with some chunks
present and others not.
Both the directory and webdav special remotes used to have to buffer
the whole file contents before it could be decrypted, as they read
from chunks. Now the chunks are streamed through gpg with no buffering.
This allows deleting all chunks for a file with a single http command,
so it's a win after all.
However, does not look in the mixed case hash directories, which were
in the past used by the directory, etc remotes.
The benefit of using a compatable directory structure does not outweigh the
cost in complexity of handling the multiple locations content can be stored
in directory special remotes. And this also allows doing away with the parent
directories, which can't be made unwritable in DAV, so have no benefit
there. This will save 2 http calls per file store.
But, kept the directory hashing, just in case.
