Fix C++ compile error in cmd0.c

Add a cast for a void *.
Fix C++ compile errors - invalid file_open parameter type.

Moot because file_open() ignores the parameter, but the compiler still
flags it.
Replace C++ reserved words in game-event.c

Replace uses of 'this' and 'new'.
Fix C++ compiler error in game_event.c

Add a required cast.
Fix C++ compiler errors in init1.c

Add required casts.