[1.7.x] Fixed typos in docs (django.contrib.site)

Backport of 907ac64641 from master.

docs/ref/contrib/sites.txt

@@ -389,7 +389,7 @@ If you often use this pattern::
         ...
 
 there is simple way to avoid repetitions. Add
-:class:`django.contrib.site.middleware.CurrentSiteMiddleware` to
+:class:`django.contrib.sites.middleware.CurrentSiteMiddleware` to
 :setting:`MIDDLEWARE_CLASSES`. The middleware sets the ``site`` attribute on
 every request object, so you can use ``request.site`` to get the current site.
 

docs/ref/middleware.txt

@@ -182,7 +182,7 @@ Enables session support. See the :doc:`session documentation
 Site middleware
 ---------------
 
-.. module:: django.contrib.site.middleware
+.. module:: django.contrib.sites.middleware
   :synopsis: Site middleware.
 
 .. class:: CurrentSiteMiddleware

docs/releases/1.7.txt

@@ -391,7 +391,7 @@ Minor features
 :mod:`django.contrib.sites`
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-* The new :class:`django.contrib.site.middleware.CurrentSiteMiddleware` allows
+* The new :class:`django.contrib.sites.middleware.CurrentSiteMiddleware` allows
   setting the current site on each request.
 
 :mod:`django.contrib.staticfiles`