better prevention of inventory relaying during initial download,

message checksum between nodes with 0.2.9 or higher,
optimization level up from -O0 to -O2,
rpc functions: setlabel, getlabel, getaddressesbylabel, getreceivedbyaddress, getreceivedbylabel, listreceivedbyaddress, listreceivedbylabel
 -- version 0.2.9

util.cpp

@@ -250,11 +250,6 @@ string strprintf(const char* format, ...)
         if (p == NULL)
             throw std::bad_alloc();
     }
-#ifdef _MSC_VER
-    // msvc optimisation
-    if (p == buffer)
-        return string(p, p+ret);
-#endif
     string str(p, p+ret);
     if (p != buffer)
         delete p;