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/attrib.c

@@ -152,7 +152,7 @@ adjattrib(ndx, incr, msgflg)
 	    You_feel("%s%s!",
 		  (incr > 1 || incr < -1) ? "very ": "",
 		  (incr > 0) ? plusattr[ndx] : minusattr[ndx]);
-	flags.botl = 1;
+	context.botl = 1;
 	if (moves > 1 && (ndx == A_STR || ndx == A_CON))
 		(void)encumber_msg();
 	return TRUE;