Log Message:
Update to 4.1.15

Changelog:
NSD 4.1.15
Feb 16, 2017

Bugfixes
    Fix nsd-control and ipv6 only.
    Squelch zone transfer error address family not supported by protocol at low \ 
verbosity levels.
    Fix #1195: Fix so that NSD fails on non-compliant values for Serial.
    Fix to rename _t typedefs because POSIX reserves them.
    Fix that nsec3 hash collisions only reported on verbosity level 3.