Replace use of OSError aliases with OSError (IOError, EnvironmentError, WindowsError, mmap.error, socket.error, select.error)

[Jon Dufresne]

Starting with Python 3.3, EnvironmentError, IOError, WindowsError, socket.error, select.error and mmap.error are aliases of OSError. With this in mind, the Django code base can be cleaned up.

For additional details, see the Python 3.3 release notes:

​https://docs.python.org/3/whatsnew/3.3.html#pep-3151-reworking-the-os-and-io-exception-hierarchy

You don’t have to worry anymore about choosing the appropriate exception type between OSError, IOError, EnvironmentError, WindowsError, mmap.error, socket.error or select.error. All these exception types are now only one: OSError. The other names are kept as aliases for compatibility reasons.

Additionally, since Python 3.4, SMTPException is subclass of OSError . So exception handles catching both can be simplified to just OSError.

​https://docs.python.org/3/library/smtplib.html#smtplib.SMTPException

Subclass of OSError that is the base exception class for all the other exceptions provided by this module.

Changed in version 3.4: SMTPException became subclass of OSError

[Jon Dufresne]

​https://github.com/django/django/pull/10904

[Nick Pope]

Now we're targeting Python ≥ 3.6 for Django 3.0 this is a nice clean up.

[Tim Graham <timograham@…>]

In 7785e03b:

Fixed #30137 -- Replaced OSError aliases with the canonical OSError.

Used more specific errors (e.g. FileExistsError) as appropriate.

[GitHub <noreply@…>]

In 9a0cc54:

Refs #30137 -- Fixed template test on Windows.

Broken in 7785e03ba89aafbd949191f126361fb9103cb980.