Release 4.3: DB_ENV->set_errcall, DB->set_errcall

The signature of the error callback passed to the DB_ENV->set_errcall() and DB->set_errcall() methods has changed in the 4.3 release. For example, if you previously had a function such as this:

void handle_db_error(const char *prefix, char *message);

it should be changed to this:

void handle_db_error(const DB_ENV *dbenv,
    const char *prefix, const char *message);

This change adds the DB_ENV handle to provide database environment context for the callback function, and incidentally makes it clear the message parameter cannot be changed by the callback.