does not already contain N if the insert cursor points to N-1. Fix for ticket
[61fe9745].
FossilOrigin-Name: 1c1b0862236f564283be08338790d6494e705f1198547a59499e3f8c07f2cd99
Add test cases for IN processing that would have spotted the error in the
[2be661a48023f4] check-in.
FossilOrigin-Name: 5ded9b68388f4024425c11f09b03529ac89454ce