Pickler enters infinite recursion with self-referential classes

The pickler recurses infinitely and dies with maximum recursion limit exceeded when a module contains a self-referential class (or any class which is part of a cycle).

Here's a minimal example: 
```

class RecursiveClass(object):
SELF_TYPE = None

def __init__(self, datum)
self.datum = 'RecursiveClass:%s'
% datum

RecursiveClass.SELF_TYPE = RecursiveClass

```

If this is in a module, then the pickler will enter the infinite recursion when trying to pickle any nested class in that module.
 

An actual example is with typing.Type, which is part of a cycle typing.Type -\> type -\> object -\> typing.Type. If a module contains an attribute that refers to typing.Type, such as a type alias, it will trigger this bug.

Imported from Jira [BEAM-4036](https://issues.apache.org/jira/browse/BEAM-4036). Original Jira may contain additional context.
Reported by: chuanyu.