Add clarifications in the documentation of the `query` command

- Add a statement that the result is always for the latest patch set,
  even if the query matched on an earlier patch set

- Add a link to the change attribute documentation from the JSON
  format option description.

- Add clarification in the change attribute documentation that the
  commit message is of the latest patch set.

- Correct a minor typo

Change-Id: Ie6a825d1d183994926662c0ad8c42ec15f687e51
diff --git a/Documentation/json.txt b/Documentation/json.txt
index 3659ed3..3893e3f 100644
--- a/Documentation/json.txt
+++ b/Documentation/json.txt
@@ -28,7 +28,8 @@
 
 url:: Canonical URL to reach this change.
 
-commitMessage:: The full commit message for the change.
+commitMessage:: The full commit message for the change's current patch
+set.
 
 createdOn:: Time in seconds since the UNIX epoch when this change
 was created.