BASIC_TYPE_SERIALIZER __int64 fix

Flann was causing an error when building against VS2015. Aparentely the
basic serializer for __int64 is being defined twice.

src/cpp/flann/util/serialization.h

@@ -109,7 +109,7 @@ BASIC_TYPE_SERIALIZER(bool);
 #ifdef _MSC_VER
 // unsigned __int64 ~= unsigned long long
 // Will throw error on VS2013
-#if _MSC_VER != 1800
+#if _MSC_VER < 1900
 BASIC_TYPE_SERIALIZER(unsigned __int64);
 #endif
 #endif