working on DTD validation on top of xml reader interfaces. Allows to

* testReader.c xmlreader.c valid.c include/libxml/tree.h
  include/libxml/valid.h include/libxml/xmlreader.h: working on
  DTD validation on top of xml reader interfaces. Allows to
  validate arbitrary large instances. This required some extensions
  to the valid module interface and augmenting the size of xmlID
  and xmlRef structs a bit.
* uri.c xmlregexp.c: simple cleanup.
Daniel
diff --git a/xmlregexp.c b/xmlregexp.c
index 129c126..481837b 100644
--- a/xmlregexp.c
+++ b/xmlregexp.c
@@ -2455,7 +2455,7 @@
 
 /**
  * xmlRegExecPushString:
- * @exec: a regexp execution context
+ * @exec: a regexp execution context or NULL to indicate the end
  * @value: a string token input
  * @data: data associated to the token to reuse in callbacks
  *