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.

 prefix=@prefix@

 exec_prefix=@exec_prefix@

 libdir=@libdir@

 includedir=@includedir@

 Name: @PACKAGE_NAME@

 Description: Library for Efficient Modeling and Optimization in Networks

 Version: @PACKAGE_VERSION@

 Libs: -L${libdir} -lemon @GLPK_LIBS@ @CPLEX_LIBS@ @SOPLEX_LIBS@ @CLP_LIBS@ @CBC_LIBS@

 Cflags: -I${includedir}