Minor changes to the "migratefiles" command

Files that were previously mirrored are no longer mentioned in the "--verbosity 1" output.  I've also added a brief summary giving the count of the files transferred and the number of errors.

There is a fix for the "reclaim" and "ensure" subcommands so that they don't give up on the first datafile they can't transfer.

There is a performance improvement to the "mirror" subcommand to remove an unnecessary "verify" when a datafile has already been mirrored.