repositioned #include for libxml.h to avoid compilation error on some

* testAutomata.c, testRegexp.c, testThreads.c, testThreadsWin32.c,
  xmlwriter.c: repositioned #include for libxml.h to avoid
  compilation error on some architectures (bug #398277)

svn path=/trunk/; revision=3578
diff --git a/testRegexp.c b/testRegexp.c
index ff9c0fc..d5228b3 100644
--- a/testRegexp.c
+++ b/testRegexp.c
@@ -6,9 +6,10 @@
  * Daniel Veillard <veillard@redhat.com>
  */
 
-#include <string.h>
 #include "libxml.h"
 #ifdef LIBXML_REGEXP_ENABLED
+#include <string.h>
+
 #include <libxml/tree.h>
 #include <libxml/xmlregexp.h>