Incorrect rendering of boolean attributes in combination with tal:attributes expression

[petschki]

We're investigating a reindering problem with boolean attributes in combination with tal:attributes expressions:

correct behavior

Input markup	Rendered markup
<input disabled="" />	<input disabled="disabled" />
<input disabled />	<input disabled="disabled" />
<input disabled="" tal:attributes="disabled python:False" />	<input />
<input disabled tal:attributes="disabled python:False" />	<input />

wrong rendering

Input markup	Rendered markup
<input disabled tal:attributes="disabled python:True" />	<input disableddisabled="" />

Background: Our code formatting tool zpretty changes all empty valued boolean attributes to "attribute without value" ... see collective/zpretty#123