Make sure yahttp is linked into remotebackend

Make sure that the yahttp directory is built first
and then link in the resulting library.

Checked with readelf -s .libs/libremotebackend.so | grep NOTYPE
that this fixes the undefined symbol.

Fixes #1732
Mydnsbackend depends on smysql from gymsqlbackend

Fixes #1738
Bail out if geoip and yaml libs are not installed
Detect cdb on OSX

cdb from homebrew doesn't ship a .pc file
so detect it the old-fashioned way.
Merge pull request #1742 from rubenk/detect-cdb-on-osx

Detect cdb on OSX
also dist dnsdist.1
Merge pull request #1739 from rubenk/link-yahttp-into-remotebackend

Make sure yahttp is linked into remotebackend
Merge pull request #1740 from rubenk/fix-mydnsbackend

Mydnsbackend depends on smysql from gymsqlbackend
Merge pull request #1741 from rubenk/check-geoip

Bail out if geoip and yaml libs are not installed