Misc DB fixes (5.1DEV__17)

This combines a number of small DB changes before the next round of large breaking modifications:

 * http://trac.openmicroscopy.org.uk/ome/ticket/12610
    * Recently reported bug in which long host names overrun the 256 character limit of the `node.conn` column. This simply widens the value. Reproducing this is difficult at best.