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.

 AM_CXXFLAGS = $(WARNINGCXXFLAGS)

 AM_CPPFLAGS = -I$(top_srcdir) -I$(top_builddir)

 LDADD = $(top_builddir)/lemon/libemon.la

 EXTRA_DIST = \

 	CMakeLists.txt \

 	digraph.lgf

 noinst_PROGRAMS = \

 	arg_parser_demo \

 	graph_to_eps_demo \

 	lgf_demo

 arg_parser_demo_SOURCES = arg_parser_demo.cc

 graph_to_eps_demo_SOURCES = graph_to_eps_demo.cc

 lgf_demo_SOURCES = lgf_demo.cc