When updating F6:
  Updating  : caching-nameserver           ####################### [11/39] 
/usr/sbin/bind-chroot-admin: line 224: [: : unary operator expected
  Updating  : bind-chroot                  ####################### [17/39] 
/usr/sbin/bind-chroot-admin: line 224: [: : unary operator expected

I think that's because I have SELinux disabled, otherwise this part of
master_zone_writes_enabled( ) wouldn't ever be interpreted.

I also think it's sufficient to get rid of "[yY1]*" (which is incorrect anyhow,
even if /usr/bin/[ would interpret regular expressions) and leave only:
if [ "$ENABLE_ZONE_WRITE" ]; then
This way, of course, even "no" is interpreted as "yes", but that's how
DISABLE_NAMED_DBUS is interpreted, as well. That's why I think it's enough :)