VERSION_COMPATIBILITY must be defined
Set version of UnNetHackPlus to 4.7.0, allow loading saves from UnNetHack

Compatible* versions of UnNetHack and UnNetHackPlus may form disjointed sets and it will not be a problem.

*as in "UnNetHackPlus may load save" UnNetHack will not be and should not be able to load UnNetHackPlus saves.
changelog updated - mention attempts to improve code quality