The heuristic for duplicate nodes contains a few typos, and
apparently slows down the solve for specs that have a lot of
sub-optimal choices to be taken.
This is likely because with a lot of sub-optimal choices, the
low priority, flawed heuristic is being used by clingo.
Here I split the heuristic, so complex rules that matter only
if we allow multiple nodes from the same package are used
only in that case.
e0059ef961