[1.7.x] Added release note about strip_tags improvement

Backport of 1c8dbb0cc from master.

docs/releases/1.6.3.txt

@@ -23,3 +23,6 @@ several bugs in 1.6.2:
   :class:`~django.forms.IntegerField` subclasses from being overwritten by the
   code in their ``__init__`` method
   (`#22245 <http://code.djangoproject.com/ticket/22245>`_).
+
+* Improved :func:`~django.utils.html.strip_tags` accuracy (but it still cannot
+  guarantee an HTML-safe result, as stated in the documentation).

docs/releases/1.7.txt

@@ -792,6 +792,12 @@ Tests
 * The database settings for testing have been collected into a dictionary
   named :setting:`TEST <DATABASE-TEST>`.
 
+Utilities
+^^^^^^^^^
+
+* Improved :func:`~django.utils.html.strip_tags` accuracy (but it still cannot
+  guarantee an HTML-safe result, as stated in the documentation).
+
 Validators
 ^^^^^^^^^^