Add type bounds to ObjectContext.localObject

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1509273 13f79535-47bb-0310-9956-ffa450edef68
Allow an Ordering subclass to be used where Ordering is accepted

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1509274 13f79535-47bb-0310-9956-ffa450edef68