Bump PowerDNS Authoritative DNS Server to 4.2.0. Release changelong can be found at
https://doc.powerdns.com/authoritative/changelog/4.2.html#change-4.2.0

Compile Tested: OpenWRT Snapshot - armv7
Run Tested: Linksys WRT1900ACS - package runs correctly, not all functionality has been tested.

Signed-off-by: James Taylor <james@jtaylor.id.au>

Maintainer: me

Compile tested: armv7l, OpenWRT SDK
Run tested: armv7l Linksys WRT1900ACS, OpenWrt SNAPSHOT, r9987-655fff1571 -
confirmed PowerDNS server links correctly against libraries. I'm unable to test
all the backend modules as I don't have suitable backing stores set up for each.

Description:
PowerDNS is a versatile nameserver which supports a large number of different
backends ranging from simple zonefiles to relational databases and load
balancing/failover algorithms. PowerDNS tries to emphasize speed and security.

This commit includes the authoritative nameserver, backends and additional tools

https://www.powerdns.com/auth.html

Signed-off-by: James Taylor <james@jtaylor.id.au>