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.

 version=2

 http://lemon.cs.elte.hu/data/lemon-(.*)\.tar\.gz	debian	uupdate