Add switch for new difficulty rule

This fixes a typo in the checkpoints and passes blocks up to the last checkpoint, even though they use the old rule.

The switch to the new rule happens at block 9328 so that it is in advance of the last checkpoint.

There is no difficulty update from 9328 and 9332, so the rule can be applied early.

This means that the 9332 checkpoint is a post rule change checkpoint.