Bug fix in CapacityScaling.

Small improvements in min cost flow files.

External flow and potential maps can be used in MinCostMaxFlow.

Reimplemented Suurballe class.

- The new version is the specialized version of CapacityScaling.
- It is about 10-20 times faster than the former Suurballe algorithm
and about 20-50 percent faster than CapacityScaling.
- Doc improvements.
- The test file is also replaced.

Backport of bug fix hg 2de55e4f57a7

Test file for the min cost flow algorithms.

Small fixes and doc improvements in MinMeanCycle.

Avoid map copy in MinCostMaxFlow.

Query improvements in the min cost flow algorithms.

- External flow and potential maps can be used.
- New query functions: flow() and potential().
- CycleCanceling also provides dual solution (node potentials).
- Doc improvements.

Bug fixes

Bug fixes in min cost flow files.
Use enum type instead of static constants in NetworkSimplex to avoid
linker errors.

Put the definitions of global functions into a .cc file.

Add a cost scaling min cost flow algorithm.

Add a cost scaling algorithm, which is performing generalized
push-relabel operations. It is almost as efficient as the capacity
scaling algorithm, but slower than network simplex.

Improvements in MinCostFlow and MinCostMaxFlow.

Main changes:
- MinCostMaxFlow also provides dual solution.
- Change the name of private members to start with "_".
- Change the name of function parameters not to start with "_".
- Remove unnecessary documentation for private members.
- Doc improvements.