Rework validation context flags

Use a bitmask instead of magic values to

- keep track whether the validation context is part of a parser context
- keep track whether xmlValidateDtdFinal was called

This allows to add addtional flags later.

Note that this deliberately changes the name of a public struct member,
assuming that this was always private data never to be used by client
code.

include/libxml/valid.h

@@ -60,17 +60,17 @@ typedef void (XMLCDECL *xmlValidityWarningFunc) (void *ctx,
 
 #ifdef IN_LIBXML
 /**
- * XML_CTXT_FINISH_DTD_0:
+ * XML_VCTXT_DTD_VALIDATED:
  *
- * Special value for finishDtd field when embedded in an xmlParserCtxt
+ * Set after xmlValidateDtdFinal was called.
  */
-#define XML_CTXT_FINISH_DTD_0 0xabcd1234
+#define XML_VCTXT_DTD_VALIDATED (1u << 0)
 /**
- * XML_CTXT_FINISH_DTD_1:
+ * XML_VCTXT_USE_PCTXT:
  *
- * Special value for finishDtd field when embedded in an xmlParserCtxt
+ * Set if the validation context is part of a parser context.
  */
-#define XML_CTXT_FINISH_DTD_1 0xabcd1235
+#define XML_VCTXT_USE_PCTXT (1u << 1)
 #endif
 
 /*
@@ -90,7 +90,7 @@ struct _xmlValidCtxt {
     int                nodeMax;       /* Max depth of the parsing stack */
     xmlNodePtr        *nodeTab;       /* array of nodes */
 
-    unsigned int     finishDtd;       /* finished validating the Dtd ? */
+    unsigned int         flags;       /* internal flags */
     xmlDocPtr              doc;       /* the document */
     int                  valid;       /* temporary validity check result */