Move sys.subversion at the right place in alphabetical order,

and add a note concerning its status.

Doc/library/sys.rst

@@ -32,20 +32,6 @@ always available.
    .. versionadded:: 2.0
 
 
-.. data:: subversion
-
-   A triple (repo, branch, version) representing the Subversion information of the
-   Python interpreter. *repo* is the name of the repository, ``'CPython'``.
-   *branch* is a string of one of the forms ``'trunk'``, ``'branches/name'`` or
-   ``'tags/name'``. *version* is the output of ``svnversion``, if the interpreter
-   was built from a Subversion checkout; it contains the revision number (range)
-   and possibly a trailing 'M' if there were local modifications. If the tree was
-   exported (or svnversion was not available), it is the revision of
-   ``Include/patchlevel.h`` if the branch is a tag. Otherwise, it is ``None``.
-
-   .. versionadded:: 2.5
-
-
 .. data:: builtin_module_names
 
    A tuple of strings giving the names of all modules that are compiled into this
@@ -992,6 +978,26 @@ always available.
    replacing it, and restore the saved object.
 
 
+.. data:: subversion
+
+   A triple (repo, branch, version) representing the Subversion information of the
+   Python interpreter. *repo* is the name of the repository, ``'CPython'``.
+   *branch* is a string of one of the forms ``'trunk'``, ``'branches/name'`` or
+   ``'tags/name'``. *version* is the output of ``svnversion``, if the interpreter
+   was built from a Subversion checkout; it contains the revision number (range)
+   and possibly a trailing 'M' if there were local modifications. If the tree was
+   exported (or svnversion was not available), it is the revision of
+   ``Include/patchlevel.h`` if the branch is a tag. Otherwise, it is ``None``.
+
+   .. versionadded:: 2.5
+
+   .. note::
+      Python is now `developed <http://docs.python.org/devguide/>`_ using
+      Mercurial.  In recent Python 2.7 bugfix releases, :data:`subversion`
+      therefore contains placeholder information.  It is removed in Python
+      3.3.
+
+
 .. data:: tracebacklimit
 
    When this variable is set to an integer value, it determines the maximum number