Get rid of MSVC's __int64

Use either int64_t, uint64_t or long long and unsigned long long, defined as per C++11 standard

Minecraft.Client/AchievementPopup.h

@@ -13,7 +13,7 @@ private:
     wstring title;
     wstring desc;
     Achievement *ach;
-    __int64 startTime;
+    int64_t startTime;
     ItemRenderer *ir;
     bool isHelper;