Alphabetized imports in various docs.

Follow-up of d97cce3409 and 7d3fe36c62.

docs/ref/models/conditional-expressions.txt

@@ -48,7 +48,7 @@ keyword.
 
 Some examples::
 
-    >>> from django.db.models import When, F, Q
+    >>> from django.db.models import F, Q, When
     >>> # String arguments refer to fields; the following two examples are equivalent:
     >>> When(account_type=Client.GOLD, then='name')
     >>> When(account_type=Client.GOLD, then=F('name'))
@@ -88,7 +88,7 @@ A simple example::
 
     >>>
     >>> from datetime import date, timedelta
-    >>> from django.db.models import CharField, Case, Value, When
+    >>> from django.db.models import Case, CharField, Value, When
     >>> Client.objects.create(
     ...     name='Jane Doe',
     ...     account_type=Client.REGULAR,

docs/ref/models/database-functions.txt

@@ -979,7 +979,7 @@ than 0. If ``length`` is ``None``, then the rest of the string will be returned.
 Usage example::
 
     >>> # Set the alias to the first 5 characters of the name as lowercase
-    >>> from django.db.models.functions import Substr, Lower
+    >>> from django.db.models.functions import Lower, Substr
     >>> Author.objects.create(name='Margaret Smith')
     >>> Author.objects.update(alias=Lower(Substr('name', 1, 5)))
     1

docs/ref/models/expressions.txt

@@ -26,7 +26,7 @@ Some examples
 
 .. code-block:: python
 
-    from django.db.models import F, Count, Value
+    from django.db.models import Count, F, Value
     from django.db.models.functions import Length, Upper
 
     # Find companies that have more employees than chairs.
@@ -252,7 +252,7 @@ is null) after companies that have been contacted::
 database functions like ``COALESCE`` and ``LOWER``, or aggregates like ``SUM``.
 They can be used directly::
 
-    from django.db.models import Func, F
+    from django.db.models import F, Func
 
     queryset.annotate(field_lower=Func(F('field'), function='LOWER'))
 

docs/ref/models/instances.txt

@@ -277,7 +277,7 @@ will be stored in a special error dictionary key,
 :data:`~django.core.exceptions.NON_FIELD_ERRORS`. This key is used for errors
 that are tied to the entire model instead of to a specific field::
 
-    from django.core.exceptions import ValidationError, NON_FIELD_ERRORS
+    from django.core.exceptions import NON_FIELD_ERRORS, ValidationError
     try:
         article.full_clean()
     except ValidationError as e: