fix catz test
On freebsd, the catz test ran correctly the first time the tarball was extracted, but would fail more and more each time it was run thereafter.
@ckb helped chase it down. The reason turned out to be that slave zone files weren't being removed after each run, because clean.sh used curly braces to group the files, which is a bash-ism and not portable bourne shell.
rm -f ns3/dom{13,14}.example.db
rm -f ns{1,2,3}/catalog{1,2,3,4}.example.db
Each time the test ran, the slave zones from a previous test would be loaded, and because the serial number was already higher, the notify messages would be ignored.
Edited by Evan Hunt