Incorrect rename behavior

[jiangmf]

When running rename_external on code with both import x and from x import y, the behavior seems to be incorrect.

In the example below, the generated code will contain an NameError: name 'custom_request' is not defined

The expected output should be my_app.custom_request.get('https://google.com')

>>> import pasta
>>> from pasta.augment import rename
>>> code = """
... import requests
... from requests import Response
...
... requests.get('https://google.com')"""
>>> tree = pasta.parse(code)
>>> rename.rename_external(tree, 'requests', 'myapp.custom_request')
True
>>> print(pasta.dump(tree))

import myapp.custom_request
from myapp.custom_request import Response

custom_request.get('https://google.com')