added two new macros IS_ASCII_LETTER and IS_ASCII_DIGIT used with (html)

* include/libxml/parserInternals.h: added two new macros
  IS_ASCII_LETTER and IS_ASCII_DIGIT used with (html)
  parsing and xpath for testing data not necessarily
  unicode.
* HTMLparser.c, xpath.c: changed use of IS_LETTER_CH and
  IS_DIGIT_CH macros to ascii versions (bug 153936).
diff --git a/HTMLparser.c b/HTMLparser.c
index 10f8516..72a0870 100644
--- a/HTMLparser.c
+++ b/HTMLparser.c
@@ -2168,11 +2168,11 @@
     int i = 0;
     xmlChar loc[HTML_PARSER_BUFFER_SIZE];
 
-    if (!IS_LETTER_CH(CUR) && (CUR != '_') &&
+    if (!IS_ASCII_LETTER(CUR) && (CUR != '_') &&
         (CUR != ':')) return(NULL);
 
     while ((i < HTML_PARSER_BUFFER_SIZE) &&
-           ((IS_LETTER_CH(CUR)) || (IS_DIGIT_CH(CUR)) ||
+           ((IS_ASCII_LETTER(CUR)) || (IS_ASCII_DIGIT(CUR)) ||
 	   (CUR == ':') || (CUR == '-') || (CUR == '_'))) {
 	if ((CUR >= 'A') && (CUR <= 'Z')) loc[i] = CUR + 0x20;
         else loc[i] = CUR;