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/spell.c

@@ -799,12 +799,12 @@ boolean atme;
 	if (confused || (rnd(100) > chance)) {
 		You("fail to cast the spell correctly.");
 		u.uen -= energy / 2;
-		flags.botl = 1;
+		context.botl = 1;
 		return(1);
 	}
 
 	u.uen -= energy;
-	flags.botl = 1;
+	context.botl = 1;
 	exercise(A_WIS, TRUE);
 	/* pseudo is a temporary "false" object containing the spell stats */
 	pseudo = mksobj(spellid(spell), FALSE, FALSE);
@@ -928,7 +928,7 @@ boolean atme;
 		if (Slimed) {
 		    pline_The("slime disappears!");
 		    Slimed = 0;
-		 /* flags.botl = 1; -- healup() handles this */
+		 /* context.botl = 1; -- healup() handles this */
 		}
 		healup(0, 0, TRUE, FALSE);
 		break;