Use the same maximum length for tags given on the command line and
tags entered in the GUI.

diff --git a/programs/winetest/winetest.h b/programs/winetest/winetest.h
index dbc1e1c..79fd43e 100644
--- a/programs/winetest/winetest.h
+++ b/programs/winetest/winetest.h
@@ -57,6 +57,7 @@
     R_QUIET
 };
 
+#define MAXTAGLEN 20
 extern char *tag;
 int guiAskTag (void);
 int report (enum report_type t, ...);