(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/3rdparty/squirrel/include/squirrel.h

@@ -275,6 +275,7 @@ typedef struct tagSQRegFunction{
 }SQRegFunction;
 
 /*vm*/
+SQUIRREL_API bool sq_can_suspend(HSQUIRRELVM v);
 SQUIRREL_API HSQUIRRELVM sq_open(SQInteger initialstacksize);
 SQUIRREL_API HSQUIRRELVM sq_newthread(HSQUIRRELVM friendvm, SQInteger initialstacksize);
 SQUIRREL_API void sq_seterrorhandler(HSQUIRRELVM v);

src/3rdparty/squirrel/squirrel/sqapi.cpp

@@ -90,6 +90,11 @@ SQInteger sq_getvmstate(HSQUIRRELVM v)
 	}
 }
 
+bool sq_can_suspend(HSQUIRRELVM v)
+{
+	return v->_can_suspend;
+}
+
 void sq_seterrorhandler(HSQUIRRELVM v)
 {
 	SQObject o = stack_get(v, -1);