OAK-666 Javadocs, improved exception message

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1453926 13f79535-47bb-0310-9956-ffa450edef68
OAK-127: initial version of session import

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1453985 13f79535-47bb-0310-9956-ffa450edef68
OAK-127: initial version of session import

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1453987 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'trunk' of github.com:apache/jackrabbit-oak into trunk
test