CAY-1911 BatchQuery refactoring - make Iterable

preliminary refactoring - localizing Oracle LOB hacks, makign them private to OracleAdapter
and unrolling batch iteration wrapper

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1577571 13f79535-47bb-0310-9956-ffa450edef68