"\xNN;" inline hex escapes should also support uppercase \X.

Fixes issue #347.

lib/srfi/38.scm

@@ -273,7 +273,7 @@
                 ((#\newline) (skip-horizontal-whitespace in) #f)
                 ((#\space #\tab)
                  (skip-line in) (skip-horizontal-whitespace in) #f)
-                ((#\x)
+                ((#\x #\X)
                  (let* ((n (read-number 16))
                         (ch2 (read-char in)))
                    (if (not (and n (eqv? ch2 #\;)))

sexp.c

@@ -2177,7 +2177,7 @@ sexp sexp_read_string (sexp ctx, sexp in, int sentinel) {
       case 'n': c = '\n'; break;
       case 'r': c = '\r'; break; 
       case 't': c = '\t'; break;
-      case 'x':
+      case 'x': case 'X':
         res = sexp_read_number(ctx, in, 16, 0);
         if (sexp_fixnump(res)) {
           c = sexp_read_char(ctx, in);