[1.7.x] Bump version number for 1.7 alpha 1.
We should branch after the first beta.

We did this for 1.6 and it was very effective. 95%+ of fixes which merge
during the alpha are backported, as the policy is "all but really major
features". It's easier to just not merge any really major features.
After beta, we have feature freeze so we need to backport bugs to stable
but not features, so then the branch makes sense.
Add docs about converting from South
Fixed some punctuation; thanks Chris Jerdonek.
Fixed #21861 -- Fixed typo in 1.7 release notes.

Thanks marktranchant.
Fixes #21864: Close string in example of custom lookups doc page.
Fixed #21864 -- Fixed missing quote in custom lookup example.

Thanks to Chris Barna for the report.
Merge pull request #2205 from ctbarna/21864-custom-lookup-unclosed-string

Fixes #21864: Close string in example of custom lookups doc page.
Fixed #21847 -- Clarified where ContactForm was defined
We should branch after the first beta.

We did this for 1.6 and it was very effective. 95%+ of fixes which merge
during the alpha are backported, as the policy is "all but really major
features". It's easier to just not merge any really major features.
After beta, we have feature freeze so we need to backport bugs to stable
but not features, so then the branch makes sense.
Merge pull request #2203 from mjtamlyn/post-beta-branching

We should branch after the first beta.
Merge branch 'stable/1.7.X'

We fork at beta. This branch will be recreated when the first beta is created.
It has been merged in to maintain the version number bump and tag.
Fixed #21865 -- Incorrect signs in documented example.

Maths is hard.