Rename function to avoid ambiguity on platforms where va_list is void *.

Index: src/lib/barrier/ProtocolUtil.h
--- src/lib/barrier/ProtocolUtil.h.orig
+++ src/lib/barrier/ProtocolUtil.h
@@ -79,7 +79,8 @@ class ProtocolUtil { (private)
                             const char* fmt, va_list);
 
     static UInt32        getLength(const char* fmt, va_list);
-    static void            writef(void*, const char* fmt, va_list);
+    /* renamed to avoid ambiguity on platforms where va_list is void * */
+    static void            writef_(void*, const char* fmt, va_list);
     static UInt32        eatLength(const char** fmt);
     static void            read(barrier::IStream*, void*, UInt32);
 };