DERBY-6751: Prevent user code from getting a LanguageConnectionContext out of an EmbedConnection; tests passed cleanly on derby-6751-01-ad-usederbyinternals.diff.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1628855 13f79535-47bb-0310-9956-ffa450edef68