fixed a couple of problems in the new elfgcchack.h trick pointed by Peter

* libxml.h uri.c: fixed a couple of problems in the new
  elfgcchack.h trick pointed by Peter Breitenlohner
Daniel
diff --git a/uri.c b/uri.c
index f36eb9c..31e51a3 100644
--- a/uri.c
+++ b/uri.c
@@ -46,10 +46,12 @@
  */
 #define IS_UPALPHA(x) (((x) >= 'A') && ((x) <= 'Z'))
 
+#ifdef IS_DIGIT
+#undef IS_DIGIT
+#endif
 /*
  * digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
  */
-
 #define IS_DIGIT(x) (((x) >= '0') && ((x) <= '9'))
 
 /*