XInclude and other stuff while travelling. Contributed patches:

- tree.[ch] xinclude.[ch] xmllint.c configure.in valid.c
  debugXML.c xmlversion.h.in: Started adding XInclude support,
  this is a new xmllint option
- tree.c xpath.c: applied TOM patches for XPath
- xpointer.c: fixed a couple of errors.
- uri.c: added an escaping function needed for xinclude
- testXPath.c hash.c HTMLtree.c: minor cleanups raised by
  new warning from RH70 gcc's version
Daniel

testXPath.c

@@ -41,6 +41,7 @@
 #include <libxml/debugXML.h>
 #include <libxml/xmlmemory.h>
 #include <libxml/parserInternals.h>
+#include <libxml/xpathInternals.h>
 #include <libxml/xmlerror.h>
 #if defined(LIBXML_XPTR_ENABLED)
 #include <libxml/xpointer.h>