* Make move command check for overlapping remotes and refuse to run
* Do copy/delete rather than all the copies then all the deletes
* Doesn't purge the source - this was unexpected behaviour see #512 and #416
* Add -list-retries flag to test suite to control retries
This changes the semantics of `move` slightly. However it now errs on
the side of not deleting stuff.
* Factor sync/copy/move into its own file
* Make fatal errors abort the sync
* Make Copy return errors
* Make Sync/Copy/Move return the last Copy error if there was one
* Prioritise returning Fatal errors
* NoRetry errors are returned if no other types of errors
