configure.in: Add support for detecting BerkeleyDB 4.6.
configure.in: Add support for detecting BerkeleyDB 4.6.

sit/dht,sit/dht,weidezhang/dht,weidezhang/dht,sit/dht,weidezhang/dht,sit/dht,weidezhang/dht,sit/dht,weidezhang/dht