Typos in 1.7 release notes

[aruseni]

First:

In addition, any clashing fields in the model inheritance hierarchy results in a system check error.

Second:

After upgrading to Django 1.7, the first request to any previously cached URL will be a cache miss .

Third:

Third-party database backends needing this functionality should modify their backends to provide an implementation of check_field().

[Tim Graham]

I don't see a typo in the first sentence. I see the extra space before the period in the second. I believe the issue in the third is that the second "backends" should be "backend" -- can you confirm?

[wraus]

I'm guessing the first sentence is "results"- you have "any clashing fields (...) results", which is incorrect, and should read "any clashing fields (...) result". Not sure what the issue is in the third sentence.

[Tim Graham <timograham@…>]

In d5a109f6e6684b2ea8028af5c57f4257872d11aa:

Fixed #23802 -- Typos in 1.7 release notes.

[Tim Graham <timograham@…>]

In cf5e2c46f2122c19c60f74299275f6fbcdd9144b:

[1.7.x] Fixed #23802 -- Typos in 1.7 release notes.

Backport of d5a109f6e6684b2ea8028af5c57f4257872d11aa from master