check_dig: Fix to work with dig and drill tool

FreeBSD starting with version 10 is shipped with ldns instead of bind as
resolver. Consequently the dig tool in base is replaced by drill. While dig can
still be installed as a third party application, it would be nice to make do
with the tools available in the system already.
This patch rearranges the command line used to invoke dig slightly so that it
can be used with both dig and drill (tested with dig 9.8.3-P1 and 9.9.4 as well
as drill 1.6.16). It would be really neat if the configure script could be
changed to automatically pick up drill when dig is not available (or the other
way around), but my autotools-foo is not good enough for that.
This part of the patch is an extended version of the locally maintained patch
currently deployed in the FreeBSD ports tree by Dmitry Sivachenko.
check_dig: takes into account the -4 and -6 switch

Fix automatic DNS server name detection to honor -4 and -6 switches
(default to 127.0.0.1 or ::1 respectively, i.e. if -6 is given ::1
is used instead of 127.0.0.1)
Adding Alexander Wittig to THANKS.in
---
Closes #1218
Closes #1281
Merge pull request #1281 from waja/github1218