a lot of small cleanups based on Linus' sparse check output. Daniel

* HTMLparser.c SAX2.c encoding.c globals.c parser.c relaxng.c
  runsuite.c runtest.c schematron.c testHTML.c testReader.c
  testRegexp.c testSAX.c testThreads.c valid.c xinclude.c xmlIO.c
  xmllint.c xmlmodule.c xmlschemas.c xpath.c xpointer.c: a lot of
  small cleanups based on Linus' sparse check output.
Daniel
diff --git a/xinclude.c b/xinclude.c
index ab64096..b6ec353 100644
--- a/xinclude.c
+++ b/xinclude.c
@@ -237,7 +237,7 @@
 	ret->URI = xmlStrdup(URI);
     ret->fragment = NULL;
     ret->ref = ref;
-    ret->doc = 0;
+    ret->doc = NULL;
     ret->count = 0;
     ret->xml = 0;
     ret->inc = NULL;
@@ -360,7 +360,7 @@
     else
         ctxt->url = NULL;
     ret = ctxt->urlTab[ctxt->urlNr];
-    ctxt->urlTab[ctxt->urlNr] = 0;
+    ctxt->urlTab[ctxt->urlNr] = NULL;
     if (ret != NULL)
 	xmlFree(ret);
 }
@@ -1952,7 +1952,7 @@
 static xmlNodePtr
 xmlXIncludePreProcessNode(xmlXIncludeCtxtPtr ctxt, xmlNodePtr node) {
     xmlXIncludeAddNode(ctxt, node);
-    return(0);
+    return(NULL);
 }
 
 /**