Reimplemented MinMeanCycle to be much more efficient.
The new version implements Howard's algorithm instead of Karp's algorithm and
it is at least 10-20 times faster on all the 40-50 random graphs we have tested.

@nodeset

label

0

1

2

3

4

5

6

@edgeset

        weight

0   3   1

0   4   1

1   5   1

5   2   1

6   2   1

0   1   1

2   1   1

3   4   1

4   5   1

5   6   1

@end