Do not compile dig with DIG_SIGCHASE; delv is better

The DIG_SIGCHASE option was needed to get dig to do DNSSEC validation. However, it never worked too well, and sometimes failed. This is why this option was not enabled by default, and had to be turned on at compile time.

In BIND 9.10, ISC introduced a new tool called "delv". This new tool uses the same validation library as the BIND server itself, and performs DNSSEC validation properly, and provides much better output too. ISC recommends that people use delv instead of dig with the SIGCHASE option. So I think it's better not to compile dig with SIGCHASE any more.