trunk only: preserving context (sys files)

Pat Rankin wrote:
> collect them all into some new struct and
> save that separately rather than jamming more non-option stuff
> into struct flags.

This patch:
- collects all context/tracking related fields from flags
  into a new structure called "context."
It also adds the following to the new structure:
- stethoscope turn support
- victual support
- tin support

sys/msdos/Makefile.BC

@@ -860,8 +860,8 @@ DECL_H      = $(INCL)\quest.h $(INCL)\spell.h $(INCL)\color.h \
 
 CONFIG_H    = $(INCL)\config1.h $(INCL)\tradstdc.h $(INCL)\coord.h $(PCCONF_H) \
 	      $(INCL)\config.h
-HACK_H      = $(CONFIG_H) $(INCL)\dungeon.h $(INCL)\align.h $(INCL)\monsym.h \
-              $(INCL)\mkroom.h $(INCL)\objclass.h $(DECL_H) \
+HACK_H      = $(CONFIG_H) $(INCL)\context.h $(INCL)\dungeon.h $(INCL)\align.h \
+	      $(INCL)\monsym.h $(INCL)\mkroom.h $(INCL)\objclass.h $(DECL_H) \
 	      $(INCL)\timeout.h $(INCL)\trap.h $(INCL)\flag.h $(INCL)\rm.h \
 	      $(INCL)\vision.h $(INCL)\mondata.h $(INCL)\wintype.h \
 	      $(INCL)\engrave.h $(INCL)\rect.h $(EXTERN_H) \