branches/zip: btr_store_big_rec_extern_fields(): Note that the page number

of the record containing the field reference may change.

btr/btr0cur.c

@@ -3836,7 +3836,10 @@ btr_store_big_rec_extern_fields(
 				record.  We do not store the heap
 				number of the record, because it can
 				change in page_zip_reorganize() or
-				btr_page_reorganize(). */
+				btr_page_reorganize().  However, also
+				the page number of the record may
+				change when B-tree nodes are split or
+				merged. */
 				mlog_write_ulint(page
 						 + FIL_PAGE_FILE_FLUSH_LSN,
 						 space_id,