Make the calls to va_list logging functions more explicit

On some platforms va_list might be defined as something that causes
ambiguity and results in the wrong function being called.
diff --git a/common/rfb/LogWriter.h b/common/rfb/LogWriter.h
index 6b85a85..c3bb2b0 100644
--- a/common/rfb/LogWriter.h
+++ b/common/rfb/LogWriter.h
@@ -36,7 +36,7 @@
 // is assigned a particular log level.
 
 #define DEF_LOGFUNCTION(name, level) \
-  inline void name(const char* fmt, va_list ap) { \
+  inline void v##name(const char* fmt, va_list ap) { \
     if (m_log && (level <= m_level))       \
       m_log->write(level, m_name, fmt, ap);\
   } \