Rework and fix the implementation of MinMeanCycle (#179)

- Fix the handling of the cycle means.
- Many implementation improvements:
- More efficient data storage for the strongly connected
components.
- Better handling of BFS queues.
- Merge consecutive BFS searches (perform two BFS searches
instead of three).

This version is about two times faster on average and an order of
magnitude faster if there are a lot of strongly connected components.

 #define LEMON_VERSION "@PROJECT_VERSION@"

 #cmakedefine LEMON_HAVE_LONG_LONG 1

 #cmakedefine LEMON_HAVE_LP 1

 #cmakedefine LEMON_HAVE_MIP 1

 #cmakedefine LEMON_HAVE_GLPK 1

 #cmakedefine LEMON_HAVE_CPLEX 1

 #cmakedefine LEMON_HAVE_CLP 1

 #cmakedefine LEMON_HAVE_CBC 1