Major improvements in NetworkSimplex.

Main changes:
- Use -potenital[] instead of potential[] to conform to the usual
terminology.
- Use function parameter instead of #define commands to select pivot rule.
- Use much faster implementation for the candidate list pivot rule.
It is about 5-20 times faster now.
- Add a new pivot rule called "Limited Search" that is a modified
version of "Block Search". It is about 25 percent faster on rather
sparse graphs.
- By default "Limited Search" is used for sparse graphs and
"Block Search" is used otherwise. This combined method is the most
efficient on every input class.
- 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.
- Many doc improvements.

 EXTRA_DIST += \

 	tools/Makefile

 if WANT_TOOLS

 bin_PROGRAMS += \

 	tools/dim_to_lgf \

 	tools/lgf-gen

 endif WANT_TOOLS

 tools_lgf_gen_SOURCES = tools/lgf-gen.cc

 tools_dim_to_lgf_SOURCES = tools/dim_to_lgf.cc