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/worn.c

@@ -579,7 +579,7 @@ clear_bypasses()
 	    for (otmp = mtmp->minvent; otmp; otmp = otmp->nobj)
 		otmp->bypass = 0;
 	}
-	flags.bypasses = FALSE;
+	context.bypasses = FALSE;
 }
 
 void
@@ -587,7 +587,7 @@ bypass_obj(obj)
 struct obj *obj;
 {
 	obj->bypass = 1;
-	flags.bypasses = TRUE;
+	context.bypasses = TRUE;
 }
 
 void