add a search for GeoIP2 libraries in configure
- "--with-geoip" is used to enable the legacy GeoIP library. - "--with-geoip2" is used to enable the new GeoIP2 library (libmaxminddb), and is on by default if the library is found. - using both "--with-geoip" and "--with-geoip2" at the same time is an error. - an attempt is made to determine the default GeoIP2 database path at compile time if pkg-config is able to report the module prefix. if this fails, it will be necessary to set the path in named.conf with geoip-directory - Makefiles have been updated, and a stub lib/dns/geoip2.c has been added for the eventual GeoIP2 search implementation.