Import error handling

Improve error handling when an error occurs during import. Problem noticed while testing FS import.
See http://trac.openmicroscopy.org.uk/ome/ticket/10090

To test:
 * Choose an image that does not import see https://docs.google.com/spreadsheet/ccc?key=0AuqP9_Rq_HgldDNjT0ZIcHRSOUg1OFpjVUthdzM4cmc#gid=8