parser: Always copy content from entity to target.

Make sure that references from IDs are updated.

Note that if there are IDs with the same value in a document, the last
one will now be returned. IDs should be unique, but maybe this should be
addressed.

include/libxml/entities.h

@@ -55,7 +55,7 @@ struct _xmlEntity {
 
     struct _xmlEntity     *nexte;	/* unused */
     const xmlChar           *URI;	/* the full URI as computed */
-    int                    owner;	/* does the entity own the childrens */
+    int                    owner;	/* unused */
     int                    flags;       /* various flags */
     unsigned long   expandedSize;       /* expanded size */
 };