OAK-1112: Support user data in local events

Add a message argument to Root.commit() and use it to pass the current
user data (if any) from the committing session to the CommitInfos attached
to locally observed commits.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1535136 13f79535-47bb-0310-9956-ffa450edef68