catalog zones fail if a zone name contains a slash

Francisco Obispo at Uniregistry reported that a catalog zone was failing with:

Jan 22 12:19:40 ns2 named[7408]: catz: error "unexpected token" while trying to generate config for zone "0/27.145.96.64.in-addr.arpa"

This is likely due to the zone name containing a slash, which can't be used when it's expanded into a filename.

There's already code in catz.c to substitute a hash when the zone name is too long; it needs to also do so when an illegal character is found in the zone name.