(svn r16502) -Fix [FS#2935]: when an AI was suspended while in a function called (indirectly) via call/acall/pcall OpenTTD crashed. Fix this by disallowing AIs to be suspended while called via call/acall/pcall.

IMPORTANT FOR AI WRITERS: AIs can no longer call any DoCommand functions (change anything, build vehicles, etc.) in a function called (indirectly) via call/acall/pcall. Where possible, please rewrite your code so it doesn't use call/acall/pcall

src/ai/ai_instance.hpp

@@ -30,6 +30,7 @@ private:
 
 class AIInstance {
 public:
+	friend class AIObject;
 	AIInstance(class AIInfo *info);
 	~AIInstance();