One more pass at reducing the cost of pg_dump's new implementation:

One more pass at reducing the cost of pg_dump's new implementation:
reduce the number of times TopoSort() has to be executed by trying to
extract multiple dependency loops from each pass, instead of only one.
This saves about another factor of ten on the regression database.
This could be considered as another exercise in grokking Fred Brooks'
maxim: Representation *is* the essence of programming.