[1.6.x] Fixed #21035 -- Changed docs to treat the acronym SQL phonetically.

The documentation and comments now all use 'an' to
refer to the word SQL and not 'a'.

Backport of 4d13cc56de from master

tests/backends/tests.py

@@ -402,7 +402,7 @@ class EscapingChecks(TestCase):
         self.assertEqual(cursor.fetchall()[0], ('%', '%d'))
 
     @unittest.skipUnless(connection.vendor == 'sqlite',
-                         "This is a sqlite-specific issue")
+                         "This is an sqlite-specific issue")
     def test_sqlite_parameter_escaping(self):
         #13648: '%s' escaping support for sqlite3
         cursor = connection.cursor()