Fixed #11374 -- Modified the documentation for forms.BooleanField to allow for...

Fixed #11374 -- Modified the documentation for forms.BooleanField to allow for the fact that it can be rendered using widgets other than a checkbox. Thanks to lygaret for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11236 bcc190cf-cafb-0310-a4f2-bffc1f526a37