Incorrect Python errors when using os.remove to delete a directory

[Adam Dinwoodie <adam@dinwoodie.org>]

If I use os.remove in Python to remove a directory, I expect it to fail
with an OSError on Python2 or a IsADirectoryError on Python3.  On
Python2, I get OSError, but with the wrong error code, whereas on
Python3 I get completely the wrong exception.

Simple testcases:

    $ rm -rf testdir && mkdir testdir && python -c 'import os; os.remove("testdir")'
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
    OSError: [Errno 1] Operation not permitted: 'testdir'

    $ rm -rf testdir && mkdir testdir && python3 -c 'import os; os.remove("testdir")'
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
    PermissionError: [Errno 1] Operation not permitted: 'testdir'

On my handy CentOS box, I see the following instead:

    $ rm -rf testdir && mkdir testdir && python -c 'import os; os.remove("testdir")'
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
    OSError: [Errno 21] Is a directory: 'testdir'

    $ rm -rf testdir && mkdir testdir && python3 -c 'import os; os.remove("testdir")'
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
    IsADirectoryError: [Errno 21] Is a directory: 'testdir'

Now I've realised what's going wrong I can work around it, but it'd be
nice if the correct error were raised in the first place.

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