New heuristics for MCF algorithms (#340)
and some implementation improvements.

- A useful heuristic is added to NetworkSimplex to make the
initial pivots faster.
- A powerful global update heuristic is added to CostScaling
and the implementation is reworked with various improvements.
- Better relabeling in CostScaling to improve numerical stability
and make the code faster.
- A small improvement is made in CapacityScaling for better
delta computation.
- Add notes to the classes about the usage of vector<char> instead
of vector<bool> for efficiency reasons.

 EXTRA_DIST += \

 	tools/CMakeLists.txt

 if WANT_TOOLS

 bin_PROGRAMS += \

 	tools/dimacs-solver \

 	tools/dimacs-to-lgf \

 	tools/lgf-gen

 dist_bin_SCRIPTS += tools/lemon-0.x-to-1.x.sh

 endif WANT_TOOLS

 tools_dimacs_solver_SOURCES = tools/dimacs-solver.cc

 tools_dimacs_to_lgf_SOURCES = tools/dimacs-to-lgf.cc

 tools_lgf_gen_SOURCES = tools/lgf-gen.cc