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/dothrow.c

@@ -49,7 +49,7 @@ int shotlimit;
 	if (!getdir((char *)0)) {
 		if (obj->oclass == COIN_CLASS) {
 		    u.ugold += obj->quan;
-		    flags.botl = 1;
+		    context.botl = 1;
 		    dealloc_obj(obj);
 		}
 		return(0);
@@ -1695,7 +1695,7 @@ struct obj *obj;
 	if(!u.dx && !u.dy && !u.dz) {
 #ifndef GOLDOBJ
 		u.ugold += obj->quan;
-		flags.botl = 1;
+		context.botl = 1;
 		dealloc_obj(obj);
 #endif
 		You("cannot throw gold at yourself.");