Address Windows warnings in apps/.

Reviewed-by: Richard Levitte <levitte@openssl.org>

apps/opt.c

@@ -80,8 +80,7 @@ static char prog[40];
 #if defined(OPENSSL_SYS_WIN32) || defined(OPENSSL_SYS_NETWARE)
 char *opt_progname(const char *argv0)
 {
-    int i;
-    int n;
+    size_t i, n;
     const char *p;
     char *q;