Fixed #20709 -- Allowed {% widthratio %} to accept an "as" parameter.

Thanks clay.evil@ for the suggestion.

docs/releases/1.7.txt

@@ -156,6 +156,9 @@ Minor features
   :meth:`~django.contrib.auth.models.User.email_user()` are passed to the
   underlying :meth:`~django.core.mail.send_mail()` call.
 
+* The :ttag:`widthratio` template tag now accepts an "as" parameter to capture
+  the result in a variable.
+
 Backwards incompatible changes in 1.7
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