disable one more instance of the msvc warning 4250 in new ai code

src/ai/default/ai.cpp

@@ -74,6 +74,12 @@ void idle_ai::play_turn()
 }
 
 
+#ifdef _MSC_VER
+#pragma warning(push)
+//silence "inherits via dominance" warnings
+#pragma warning(disable:4250)
+#endif
+
 /** Sample ai, with simple strategy. */
 class sample_ai : public ai::readwrite_context_proxy, public ai::interface {
 public:
@@ -221,6 +227,11 @@ private:
 	ai::recursion_counter recursion_counter_;
 };
 
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif
+
+
 ai_default::ai_default(ai::default_ai_context &context) :
 	game_logic::formula_callable(),
 	recursion_counter_(context.get_recursion_count()),