Release 4.2: DB->del

In previous releases, the C++ Db::del and Java Db.delete() methods threw exceptions encapsulating the DB_KEYEMPTY error in some cases when called on Queue and Recno databases. Unfortunately, this was undocumented behavior.

For consistency with the other Berkeley DB methods that handle DB_KEYEMPTY, this is no longer the case. Applications calling the Db::del and Java Db.delete() methods on Queue or Recno databases, and handling the DB_KEYEMPTY exception specially, should be modified to check for a return value of DB_KEYEMPTY instead.