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/teleport.c

@@ -549,7 +549,7 @@ dotele()
 			return(0);
 	    } else {
 		u.uen -= energy;
-		flags.botl = 1;
+		context.botl = 1;
 	    }
 	}
 
@@ -777,7 +777,7 @@ level_tele()
 	schedule_goto(&newlevel, FALSE, FALSE, 0, (char *)0, (char *)0);
 	/* in case player just read a scroll and is about to be asked to
 	   call it something, we can't defer until the end of the turn */
-	if (u.utotype && !flags.mon_moving) deferred_goto();
+	if (u.utotype && !context.mon_moving) deferred_goto();
 }
 
 void