branches/zip: buf_page_set_old(): Improve UNIV_LRU_DEBUG diagnostics

in order to catch the buf_pool->LRU_old corruption reported in Issue #381.

buf_LRU_old_init(): Set the property from the tail towards the front
of the buf_pool->LRU list, in order not to trip the debug check.

buf/buf0lru.c

@@ -1009,13 +1009,11 @@ buf_LRU_old_init(void)
 	the adjust function to move the LRU_old pointer to the right
 	position */
 
-	bpage = UT_LIST_GET_FIRST(buf_pool->LRU);
-
-	while (bpage != NULL) {
+	for (bpage = UT_LIST_GET_LAST(buf_pool->LRU); bpage != NULL;
+	     bpage = UT_LIST_GET_PREV(LRU, bpage)) {
 		ut_ad(bpage->in_LRU_list);
 		ut_ad(buf_page_in_file(bpage));
 		buf_page_set_old(bpage, TRUE);
-		bpage = UT_LIST_GET_NEXT(LRU, bpage);
 	}
 
 	buf_pool->LRU_old = UT_LIST_GET_FIRST(buf_pool->LRU);

include/buf0buf.ic

@@ -466,10 +466,14 @@ buf_page_set_old(
 	ut_ad(bpage->in_LRU_list);
 
 #ifdef UNIV_LRU_DEBUG
-	if (UT_LIST_GET_PREV(LRU, bpage) && UT_LIST_GET_NEXT(LRU, bpage)
-	    && UT_LIST_GET_PREV(LRU, bpage)->old
-	    == UT_LIST_GET_NEXT(LRU, bpage)->old) {
-		ut_a(UT_LIST_GET_PREV(LRU, bpage)->old == old);
+	if (UT_LIST_GET_PREV(LRU, bpage) && UT_LIST_GET_NEXT(LRU, bpage)) {
+		const buf_page_t*	prev = UT_LIST_GET_PREV(LRU, bpage);
+		const buf_page_t*	next = UT_LIST_GET_NEXT(LRU, bpage);
+		if (prev->old == next->old) {
+			ut_a(prev->old == old);
+		} else {
+			ut_a(!prev->old);
+		}
 	}
 #endif /* UNIV_LRU_DEBUG */