bpo-37150: Throw ValueError if FileType class object was passed in add_argument (GH-13805)



There is a possibility that someone (like me) accidentally will omit parentheses with `FileType` arguments after `FileType`, and parser will contain wrong file until someone will try to use it. 

Example:
```python
parser = argparse.ArgumentParser()
parser.add_argument('-x', type=argparse.FileType)
```


https://bugs.python.org/issue37150
3 files changed