trying to fix entities behaviour when using SAX, had to extend entities

* include/libxml/entities.h entities.c SAX2.c parser.c: trying to
  fix entities behaviour when using SAX, had to extend entities
  content and hack on the entities processing code, but that should
  fix the long standing bug #159219
Daniel

include/libxml/entities.h

@@ -56,6 +56,7 @@ struct _xmlEntity {
     struct _xmlEntity     *nexte;	/* unused */
     const xmlChar           *URI;	/* the full URI as computed */
     int                    owner;	/* does the entity own the childrens */
+    int			 checked;	/* was the entity content checked */
 };
 
 /*