dns/getdns: 0.1.5 -> 0.1.6

• Fix: linking against libev on FreeBSD
• Fix: Let configure report problem on FreeBSD when configuring with libevent and libunbound <= 1.4.22 is not compiled with libevent.
• Better libcheck detection
• Better portability with UNIX systems

PR: 197560
Submitted by: pi
Approved by: zi (maintainer)