[tz] tz2013a on github now, not yet at IANA

[Paul Eggert]

At this point I consider the tz version on github to be
the next official release.  I've updated its version number
accordingly, to tz2013a.  I am still working through security hassles
getting it officially installed at IANA.  The current hangup is an
incompatibility between my secure client (64-bit GNU/Linux)
and IANA's authenticator (something written by Juniper that
insists on 32-bit Java), which we have not yet ironed out.