Improve documentation and tooling around autoclose

Summary:
Fixes T4767. I believe 80% of this was actually caused by the author issue fixed in T5771, but this should help make the other 20% debuggable.

  - Record why we didn't autoclose a commit when we process it.
  - Show branch autoclose status in the main branch table.
  - Show commit autoclose status on the edit screen.
  - Add documentation about how to find these statuses and what they mean.

Test Plan:
  - Read documentation.
  - Viewed branches and hovered over the various states.
  - Viewed commits in various states and checked the "Autoclose?" field.
  - Pushed some commits and saw autoclose activate.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4767

Differential Revision: https://secure.phabricator.com/D10348

src/docs/user/userguide/diffusion_autoclose.diviner

@@ -0,0 +1,60 @@
+@title Diffusion User Guide: Autoclose
+@group userguide
+
+Explains when Diffusion will close tasks and revisions upon discovery of related
+commits.
+
+Overview
+========
+
+Diffusion can close tasks and revisions when related commits appear in a
+repository. For example, if you make a commit with `Fixes T123` in the commit
+message, Diffusion will close the task `T123`.
+
+This document explains how autoclose works, how to configure it, and how to
+troubleshoot it.
+
+Troubleshooting Autoclose
+=========================
+
+You can check if a branch is currently configured to autoclose on the main
+repository view, or in the branches list view. Hover over the {icon check} or
+{icon times} icon and you should see one of these messages:
+
+  - {icon check} **Autoclose Enabled** Autoclose is active for this branch.
+  - {icon times} **Repository Importing** This repository is still importing.
+    Autoclose does not activate until a repository finishes importing for the
+    first time. This prevents situations where you import a repository and
+    accidentally close hundreds of related objects during import. Autoclose
+    will activate for new commits after the initial import completes.
+  - {icon times} **Repository Autoclose Disabled** Autoclose is disabled for
+    this entire repository. You can enable it in **Edit Repository**.
+  - {icon times} **Branch Untracked** This branch is not tracked. Because it
+    is not tracked, commits on it won't be seen and won't be discovered.
+  - {icon times} **Branch Autoclose Disabled** Autoclose is not enabled for
+    this branch. You can adjust which branches autoclose in **Edit Repository**.
+    This option is only available in Git.
+
+If a branch is in good shape, you can check a specific commit by viewing it
+in the web UI and clicking **Edit Commit**. There should be an **Autoclose?**
+field visible in the form, with possible values listed below.
+
+Note that this field records the state of the world at the time the commit was
+processed, and does not necessarily reflect the current state of the world.
+For example, if a commit did not trigger autoclose because it was processed
+during initial import, the field will still show **No, Repository Importing**
+even after import completes. This means that the commit did not trigger
+autoclose because the repository was importing at the time it was processed,
+not necessarily that the repository is still importing.
+
+  - **Yes** At the time the commit was imported, autoclose triggered and
+    Phabricator attempted to close related objects.
+  - **No, Repository Importing** At the time the commit was processed, the
+    repository was still importing. Autoclose does not activate until a
+    repository fully imports for the first time.
+  - **No, Autoclose Disabled** At the time the commit was processed, the
+    repository had autoclose disabled.
+  - **No, Not On Autoclose Branch** At the time the commit was processed,
+    no containing branch was configured to autoclose.
+  - //Field Not Present// This commit was processed before we implemented
+    this diagnostic feature, and no information is available.