void assertOk() const {
     massert( 14809, "Invalid access for cursor that is not ok()", !_currLoc().isNull() );
 }
 DiskLoc QueryOptimizerCursorImpl::currLoc() {
     return _takeover ? _takeover->currLoc() : _currLoc();
 }
 virtual DiskLoc currLoc() { return _takeover ? _takeover->currLoc() : _currLoc(); }