textproc/htdig: Fix build with Clang 6

In file included from Configuration.cc:24:
In file included from ./Configuration.h:107:
In file included from ./Dictionary.h:22:
./htString.h:28:10: fatal error: 'iostream.h' file not found
#include <iostream.h>

^~~~~~~~~~~~

http://beefy11.nyi.freebsd.org/data/head-i386-default/p477696_s338122/logs/errors/htdig-3.2.0.b6_6.log

• Fix WWW; htdig.org seems to be gone