does the "webdrive" javascript move objects with delete-before-add?

[warner]

The 'delete sometimes appears to fail but succeeds' problem described in #550, coupled with user reports of directories disappearing during a move operation, makes me wonder if the allmydata.com javascript frontend (known as the "webdrive", and which will be copied into Tahoe some day when we get the time to make it sensibly configurable) is using delete-before-add sequencing in its "rename"/"move" operation.

Tahoe's own "mv" behavior uses add-before-delete, so that if anything goes wrong, you'll wind up with two copies of the file (or directory) being moved, rather than zero.

This ticket is just to remind me to check that the javascript frontend does the same thing.