[1.6.x] Added release note stubs for 1.5.6 and 1.4.11.

Backport of dfa28981ce from master

docs/releases/1.4.11.txt

@@ -0,0 +1,8 @@
+===========================
+Django 1.4.11 release notes
+===========================
+
+*Under development*
+
+Django's vendored version of six, :mod:`django.utils.six`, has been upgraded to
+the latest release (1.5.2).

docs/releases/1.5.6.txt

@@ -0,0 +1,15 @@
+==========================
+Django 1.5.6 release notes
+==========================
+
+*Under development*
+
+Django's vendored version of six, :mod:`django.utils.six`, has been upgraded to
+the latest release (1.5.2).
+
+Bugfixes
+========
+
+* Fixed :class:`~django.contrib.auth.backends.ModelBackend` raising
+  ``UnboundLocalError`` if :func:`~django.contrib.auth.get_user_model`
+  raised an error (#21439).

docs/releases/index.txt

@@ -31,6 +31,7 @@ Final releases
 .. toctree::
    :maxdepth: 1
 
+   1.5.6
    1.5.5
    1.5.4
    1.5.3
@@ -43,6 +44,7 @@ Final releases
 .. toctree::
    :maxdepth: 1
 
+   1.4.11
    1.4.10
    1.4.9
    1.4.8