tzdata/zic: bump to version 2013c and switch SITE

Bump to version 2013c and switch to the FTP site since the HTTP one is
unfortunately serving .tar.gz files that are just plain tar files
(uncompressed).

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>