cleaning up XPath error reporting that time. applied the two patches for

* error.c include/libxml/xmlerror.h include/libxml/xpath.h
  include/libxml/xpathInternals.h xpath.c: cleaning up XPath
  error reporting that time.
* threads.c: applied the two patches for TLS threads
  on Windows from Jesse Pelton
* parser.c: tiny safety patch for xmlStrPrintf() make sure the
  return is always zero terminated. Should also help detecting
  passing wrong buffer size easilly.
* result/VC/* result/valid/rss.xml.err result/valid/xlink.xml.err:
  updated the results to follow the errors string generated by
  last commit.
Daniel

include/libxml/xpath.h

@@ -13,6 +13,7 @@
 #define __XML_XPATH_H__
 
 #include <libxml/xmlversion.h>
+#include <libxml/xmlerror.h>
 #include <libxml/tree.h>
 #include <libxml/hash.h>
 
@@ -253,6 +254,12 @@ struct _xmlXPathContext {
     /* temporary namespace lists kept for walking the namespace axis */
     xmlNsPtr *tmpNsList;		/* Array of namespaces */
     int tmpNsNr;			/* number of namespace in scope */
+
+    /* error reporting mechanism */
+    void *userData;                     /* user specific data block */
+    xmlStructuredErrorFunc error;       /* the callback in case of errors */
+    xmlError lastError;			/* the last error */
+    xmlNodePtr debugNode;		/* the source node XSLT */
 };
 
 /*