preserve '$(' literal rendering from Genshi

Preserve Genshi's handling of '$(' as a text literal, since it cannot be a
valid variable sequence.  This simplifies, for example, templates
containing inline scripts with jQuery calls which otherwise have to be
written '$$(...'

Example template:

    <!DOCTYPE html>
    <html>
    <head>
        <title></title>
    </head>
    <body>
        <p>Test: $(</p>
    </body>
    </html>


Genshi renders the paragraph "Test: $(" while Kajiki throws an error.