[2.0.x] Fixed 'a'/'an' mix-ups in docs.

Backport of 617686e226 from master

docs/howto/custom-lookups.txt

@@ -109,7 +109,7 @@ or where it did not exceed a certain amount
     functionality which is possible in a database backend independent manner,
     and without duplicating functionality already in Django.
 
-We will start by writing a ``AbsoluteValue`` transformer. This will use the SQL
+We will start by writing an ``AbsoluteValue`` transformer. This will use the SQL
 function ``ABS()`` to transform the value before comparison::
 
   from django.db.models import Transform
@@ -257,7 +257,7 @@ operator. (Note that in reality almost all databases support both, including
 all the official databases supported by Django).
 
 We can change the behavior on a specific backend by creating a subclass of
-``NotEqual`` with a ``as_mysql`` method::
+``NotEqual`` with an ``as_mysql`` method::
 
   class MySQLNotEqual(NotEqual):
       def as_mysql(self, compiler, connection):

docs/ref/utils.txt

@@ -993,7 +993,7 @@ appropriate entities.
 
 .. function:: make_naive(value, timezone=None)
 
-    Returns an naive :class:`~datetime.datetime` that represents in
+    Returns a naive :class:`~datetime.datetime` that represents in
     ``timezone``  the same point in time as ``value``, ``value`` being an
     aware :class:`~datetime.datetime`. If ``timezone`` is set to ``None``, it
     defaults to the :ref:`current time zone <default-current-time-zone>`.

docs/topics/db/multi-db.txt

@@ -650,7 +650,7 @@ registered with any ``Admin`` instance::
 
 This example sets up two admin sites. On the first site, the
 ``Author`` and ``Publisher`` objects are exposed; ``Publisher``
-objects have an tabular inline showing books published by that
+objects have a tabular inline showing books published by that
 publisher. The second site exposes just publishers, without the
 inlines.
 

docs/topics/http/urls.txt

@@ -227,7 +227,7 @@ This usage isn't particularly recommended as it makes it easier to accidentally
 introduce errors between the intended meaning of a match and the arguments
 of the view.
 
-In either case, using only one style within an given regex is recommended. When
+In either case, using only one style within a given regex is recommended. When
 both styles are mixed, any unnamed groups are ignored and only named groups are
 passed to the view function.
 

docs/topics/testing/advanced.txt

@@ -303,7 +303,7 @@ Advanced features of ``TransactionTestCase``
     recommended that you do not hard code primary key values in tests.
 
     Using ``reset_sequences = True`` will slow down the test, since the primary
-    key reset is an relatively expensive database operation.
+    key reset is a relatively expensive database operation.
 
 .. _testing-reusable-applications: