Replace MYSQL_inc with MYSQL_CFLAGS

Part of #1748
Replace MYSQL_lib with MYSQL_LIBS

Part of #1748
Allow overriding of LDAP_LIBS

Part of #1826
Port port
docs: recursor/running: cleanup

Mark all config vars bold, all commands/parameters preformatted,
remove double escaping.
docs: recursor/running: add new(er) commands
root MX test
test NS and CNAME pointing at the root
no fancy-records in tinydns generate-data.sh
output varies between versions
mydnsbackend: fix types pointing at root
lmdbbackend: fix types pointing at root
add 'bench-db' to do very simple database backend performance benchmark
fix startup race condition with carbon thread already trying to broadcast uninitialized data
make sure we don't throw an exception on "pdns_control show" of an unknown variable
BAD_NETS taken from both:
http://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml
and
http://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml
where such a network may not be considered a valid destination
fix up latency reporting for sub-millisecond latencies (would clip to 0)
temporary gross hack, but need to test our whole build environment. If you set environment variable NOBOTAN, we won't use Botan for signing.
with thanks to Jack Lloyd, this works around the default Botan allocator slowing down for us during production use.
Fix typo in comment