Fixed #18134 -- BoundField.label_tag now includes the form's label_suffix

There was an inconsistency between how the label_tag for forms were
generated depending on which method was used: as_p, as_ul and as_table
contained code to append the label_suffix where as label_tag called on a
form field directly did NOT append the label_suffix. The code for
appending the label_suffix has been moved in to the label_tag code of
the field and the HTML generation code for as_p, as_ul and as_table now
calls this code as well.

This is a backwards incompatible change because users who have added the
label_suffix manually in their templates may now get double label_suffix
characters in their forms.

docs/ref/forms/api.txt

@@ -498,6 +498,8 @@ include ``%s`` -- then the library will act as if ``auto_id`` is ``True``.
 
 By default, ``auto_id`` is set to the string ``'id_%s'``.
 
+.. attribute:: Form.label_suffix
+
 Normally, a colon (``:``) will be appended after any label name when a form is
 rendered. It's possible to change the colon to another character, or omit it
 entirely, using the ``label_suffix`` parameter::
@@ -650,12 +652,17 @@ To separately render the label tag of a form field, you can call its
 
     >>> f = ContactForm(data)
     >>> print(f['message'].label_tag())
-    <label for="id_message">Message</label>
+    <label for="id_message">Message:</label>
 
 Optionally, you can provide the ``contents`` parameter which will replace the
 auto-generated label tag. An optional ``attrs`` dictionary may contain
 additional attributes for the ``<label>`` tag.
 
+.. versionchanged:: 1.6
+
+    The label now includes the form's :attr:`~django.forms.Form.label_suffix`
+    (a semicolon, by default).
+
 .. method:: BoundField.css_classes()
 
 When you use Django's rendering shortcuts, CSS classes are used to