CAY-1869 ResultIterator from cayenne-client dependency is subclassed from org.apache.cayenne.access.ResultIterator which is present only in cayenne-server dependency

upgrade notes
clarification in javadocs

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1523038 13f79535-47bb-0310-9956-ffa450edef68