[1.9.x] Normalized "an SQL" spelling.

Backport of 575a9a791e from master

docs/howto/custom-lookups.txt

@@ -71,7 +71,7 @@ We then need to define the ``as_sql`` method. This takes a ``SQLCompiler``
 object, called ``compiler``,  and the active database connection.
 ``SQLCompiler`` objects are not documented, but the only thing we need to know
 about them is that they have a ``compile()`` method which returns a tuple
-containing a SQL string, and the parameters to be interpolated into that
+containing an SQL string, and the parameters to be interpolated into that
 string. In most cases, you don't need to use it directly and can pass it on to
 ``process_lhs()`` and ``process_rhs()``.
 
@@ -92,7 +92,7 @@ example, ``process_lhs`` returns ``('"author"."name"', [])`` and
 parameters for the left hand side, but this would depend on the object we have,
 so we still need to include them in the parameters we return.
 
-Finally we combine the parts into a SQL expression with ``<>``, and supply all
+Finally we combine the parts into an SQL expression with ``<>``, and supply all
 the parameters for the query. We then return a tuple containing the generated
 SQL string and the parameters.
 

docs/ref/models/expressions.txt

@@ -92,7 +92,7 @@ makes it possible to refer to model field values and perform  database
 operations using them without actually having to pull them out of the  database
 into Python memory.
 
-Instead, Django uses the ``F()`` object to generate a SQL expression that
+Instead, Django uses the ``F()`` object to generate an SQL expression that
 describes the required operation at the database level.
 
 This is easiest to understand through an example. Normally, one might do

docs/releases/1.8.txt

@@ -651,7 +651,7 @@ Tests
 
 * Added test client support for file uploads with file-like objects.
 
-* A shared cache is now used when testing with a SQLite in-memory database when
+* A shared cache is now used when testing with an SQLite in-memory database when
   using Python 3.4+ and SQLite 3.7.13+. This allows sharing the database
   between threads.
 

docs/topics/testing/overview.txt

@@ -179,7 +179,7 @@ control the particular collation used by the test database. See the
 :doc:`settings documentation </ref/settings>` for details of these
 and other advanced settings.
 
-If using a SQLite in-memory database with Python 3.4+ and SQLite 3.7.13+,
+If using an SQLite in-memory database with Python 3.4+ and SQLite 3.7.13+,
 `shared cache <https://www.sqlite.org/sharedcache.html>`_ will be enabled, so
 you can write tests with ability to share the database between threads.