Performance enhancement: avoid virtual method calls, use inlined get_waytype()
Performance enhancement: ild(), set_value(), and returning 0 optimized.
Added: new file simunits.cc
Changed: moving constant definitions from simunits.h and convoy.h to their .cc files.
- Avoids multiple instantiations of these constants in all object files of source files
  that included simunits.h or convoy.h (and that were really many).
Excluded: calls to INT_CHECK() in "low level" methods.
- This is at least for debugging. Preformance profiling was almost impossible with them.
  I could not see any impact on (local) game play, although the game was really slow while profiling.
Updated: project files VC++ and Eclipse/GCC