[master] merge dyndb 4224. [func] Added support for "dyndb", a new interface for loading zone data from an external database, developed by Red Hat for the FreeIPA project. DynDB drivers fully implement the BIND database API, and are capable of significantly better performance and functionality than DLZ drivers, while taking advantage of advanced database features not available in BIND such as multi-master replication. Thanks to Adam Tkac and Petr Spacek of Red Hat. [RT #35271]