CAY-1911 BatchQuery refactoring - make Iterable

preliminary refactoring - StringBuffer -> StringBuilder

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1577549 13f79535-47bb-0310-9956-ffa450edef68
unused import

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1577550 13f79535-47bb-0310-9956-ffa450edef68