Commit #5787 makes class rest_framework.exceptions.ErrorDetail unhashable. This breaks functionality of some third-party libraries (like https://github.com/FutureMind/drf-friendly-errors).

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

from rest_framework.exceptions import ErrorDetail
err = ErrorDetail('error', code=1)
hash(err)

Expected behavior

valid hash

Actual behavior

Traceback (most recent call last):
File "", line 1, in
TypeError: unhashable type: 'ErrorDetail'