Don't interleave the tags with the branch save dates in the VFS. Doing
so meant that any access to the /branch required retrieving all tags in
the repository. It also introduced the possibility of duplicate tag and
date names.
Tags are still available in the global /.tag directory.
Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>