trunk only: preserving context (src 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

src/objnam.c

@@ -2107,13 +2107,13 @@ boolean from_user;
 		if (from_user)
 		    pline("%d gold piece%s.", cnt, plur(cnt));
 		u.ugold += cnt;
-		flags.botl=1;
+		context.botl=1;
 		return (&zeroobj);
 #else
                 otmp = mksobj(GOLD_PIECE, FALSE, FALSE);
 		otmp->quan = cnt;
                 otmp->owt = weight(otmp);
-		flags.botl=1;
+		context.botl=1;
 		return (otmp);
 #endif
 	}