btreecursor may do a lot of scanning in constructor or advance()

        /**

         * Attempt to locate the next btree key matching _bounds.  This may mean advancing to the

         * next successive key in the btree, or skipping (potentially multiple times in a single

         * function call) to a new position in the btree.  If an internal iteration cutoff is

         * reached before a matching key is found, then the search for a matching key will be

         * aborted.  This may leave the cursor pointing at a key that is not within bounds

         * (_bounds->matchesKey( currKey() ) may be false).  In that case,

         * _currentPossiblyOutOfBounds will be set to true.

         */

        void skipAndCheck();