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/mthrowu.c

@@ -205,7 +205,7 @@ boolean verbose;  /* give message(s) even when you can't see what happened */
 			(nonliving(mtmp->data) || !canspotmon(mtmp))
 			? "destroyed" : "killed");
 		/* don't blame hero for unknown rolling boulder trap */
-		if (!flags.mon_moving &&
+		if (!context.mon_moving &&
 		    (otmp->otyp != BOULDER || range >= 0 || !otmp->otrapped))
 		    xkilled(mtmp,0);
 		else mondied(mtmp);