Added some methods to PathOutageDao to fetch node IDs for nodes in the path
outage.
Better blank value checking in DefaultPollContext.
Javadoc updates.
Added method that is used by path outage code to NodeDao.
Updated the PathOutageManagerDaoImpl to simplify some code and to fix
some query problems.
Merge branch 'develop' of https://github.com/OpenNMS/opennms into develop