Constraint matches should not use object equality

This blocks some of our new features, also plenty of people are running into this in the wild and getting exceptions.

Some things that need to happen here:

• swing app: the button on bottem left for nurse rostering 3 times (1
  unsolved, 1 solves, 1 solved again)
• benchmark with the stats that use constraint match
• FULL_ASSERT, NON_INTRUSIVE_FULL_ASSERT (maybe FAST_ASSERT), CH and 20
  secs LS on diverse of examples