Any page containing a `<http://...>` link produced a
global TracError:
{{{
Genshi UnicodeEncodeError error while rendering template (unknown template location)
}}}
The code was doing something like `'...%s...' % Element()` and the
Genshi builder `Element` contained a non-ascii character (ZWSP). In
Genshi 0.7, conversion to a `str` is now producing `unicode`, as the
default encoding parameter for `Stream.render()` is now `None`
(i.e. `unicode`).
Added a test case to catch this.
