[tex-live] Using tlmgr to update TL2010 pretest

[Karl Berry]

    /usr/texbin/tlmgr: (make_container
    __BACKUP_context.universal-darwin.r16044.tar)
    bin/universal-darwin/mpstools does not exist
    ...
    concerning some doc files for moderncv. 

I wildly speculate that the backup feature (now turned on by default) is
using the current tlpdb to determine the files to back up, instead of
the tlpdb-before-update.  Norbert?

Thanks,
k