PY-19775 Fixed: Unresolved attribute reference on attribute defined inside async def __init__

Highlight builtin methods (except __aiter__, __aenter__, __aexit__, __anext__) which are not allowed to be async

python/psi-api/src/com/jetbrains/python/psi/PyFunction.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2014 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -70,6 +70,8 @@ public interface PyFunction extends PsiNamedElement, StubBasedPsiElement<PyFunct
 
   boolean isAsync();
 
+  boolean isAsyncAllowed();
+
   /**
    * Flags that mark common alterations of a function: decoration by and wrapping in classmethod() and staticmethod().
    */