- nact.h and xsystem35.h no longer include scenario.h
- Removed `sys_*` aliases in nact.h
- sys_getString() and sys_getConstString() are moved to
scenario.c as sl_getString() and sl_getConstString()
- DEBUG_COMMAND macros are now defined in scenario.h
This replaces v_str* functions with new svar_* functions.
The new svar_* functions use 1-based string variable index, so that
callers don't have to decrement string numbers from SCO.