Settings xref markup for trunk

[Ramiro Morales]

This patch converts all the bare ``SETTING_NAME`` occurrences all over the trunk documentation as of r9330 to proper :setting:SETTING_NAME constructs as per ​http://docs.djangoproject.com/en/dev/internals/documentation/#todo, except for:

• ref/settings.txt
• release/*
• internals/documentation.txt

replacements were performed with a locally modified docs/_ext/literals_to_xrefs.py script.

It applies to the 1.0.X branch as of r9331 with some fuzz:

$ patch -p1 < ../xref-markup-settings-r9330.diff 
patching file docs/faq/admin.txt
patching file docs/faq/models.txt
patching file docs/howto/deployment/fastcgi.txt
patching file docs/internals/contributing.txt
patching file docs/intro/tutorial01.txt
patching file docs/ref/contrib/admin.txt
patching file docs/ref/contrib/comments/settings.txt
patching file docs/ref/contrib/index.txt
patching file docs/ref/databases.txt
patching file docs/ref/django-admin.txt
Hunk #2 succeeded at 164 (offset 4 lines).
Hunk #3 succeeded at 185 with fuzz 1 (offset 4 lines).
Hunk #4 succeeded at 249 (offset 4 lines).
Hunk #5 succeeded at 263 (offset 4 lines).
Hunk #6 succeeded at 312 (offset 4 lines).
Hunk #7 succeeded at 347 (offset 4 lines).
Hunk #8 succeeded at 552 (offset 32 lines).
Hunk #9 succeeded at 656 (offset 32 lines).
Hunk #10 succeeded at 810 (offset 74 lines).
patching file docs/ref/forms/fields.txt
patching file docs/ref/generic-views.txt
patching file docs/ref/request-response.txt
patching file docs/ref/templates/builtins.txt
patching file docs/topics/cache.txt
patching file docs/topics/db/transactions.txt
patching file docs/topics/email.txt
patching file docs/topics/files.txt
patching file docs/topics/http/file-uploads.txt
patching file docs/topics/http/sessions.txt
patching file docs/topics/http/urls.txt
patching file docs/topics/http/views.txt
patching file docs/topics/i18n.txt
patching file docs/topics/settings.txt
patching file docs/topics/templates.txt
patching file docs/topics/testing.txt
Hunk #1 succeeded at 849 (offset -30 lines).

but Sphinx generates no warnings when running make html.