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

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.