Implement the NotEquals operator.

Somehow the NotEquals operator fell through the cracks when implementing
all the other operators.  Add it in, along with the necessary tests so it
will round trip the system properly.

git-svn-id: https://groke.mcmaster.ca/svn/grad/colin/branches/TableTool_javization@10853 57e6efec-57d4-0310-aeb1-a6c144bb1a8b