Fix a couple of bugs found in testing:
1.  It was possible to enter rubbish in the filter panel text box and get an unhandled exception.  This is now trapped.
2.  There was another place where we messed with the RowFilter without 'informing' the filter panel so resulted in wrong number of records (and probably wrong records) being displayed.
A further merge from Branch 'lp:~alan-paterson/openpetraorg/dev0001853_dec2013_release'.