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.

 #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