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
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
README.md: point people directly at the new docs
Document AXFR-SOURCE domainmetadata option
Merge pull request #1942 from rubenk/update-readme

README.md: point people directly at the new docs
Merge pull request #1943 from rubenk/document-axfr-source

Document AXFR-SOURCE domainmetadata option
Count the number of NOTIFY packets received
Only log remote nameservers

Skip the A/AAAA records.

Previously, we would log:
Unable to find backend willing to host example.com for potential supermaster x.x.x.x. 4 remote nameservers:
test1.example.com
test2.example.com
x.x.x.x
x.x.x.y
Add rping to the pdns_control manpage