versioned container switching

[Karl Berry]

    With the latest version of texlive.infra, the unversioned looks are
    not necessary, we just keep them out of nostalgy(?). [nostalgia]

They should also allow any older programs to keep working with the
"versioned" repository. Notably the installer, although I didn't go so
far as to do a full installation with an old install-tl. Anyway,
definitely no plans to remove the unversioned links. -k