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/lock.c

@@ -417,7 +417,7 @@ pick_lock(pick) /* pick a lock with a given object */
 		    xlock.box = 0;
 	    }
 	}
-	flags.move = 0;
+	context.move = 0;
 	xlock.chance = ch;
 	xlock.picktyp = picktyp;
 	xlock.usedtime = 0;