rsync is now used when copying files from repos on other filesystems

cp is still used when copying file from repos on the same filesystem, since
--reflink=auto can make it significantly faster on filesystems such as
btrfs.

Directory special remotes still use cp, not rsync. It's not clear what
tmp file should be used when rsyncing to such a remote.

doc/todo/file_copy_progress_bar.mdwn

@@ -1,3 +1,5 @@
 Find a way to copy a file with a progress bar, while still preserving
 stat. Easiest way might be to use pv and fix up the permissions etc
 after?
+
+[[done]]