Expressions not evaluated in unknown condition

This was reported on #pyramid by varesa. I haven't figured out why this breaks, but the tests do show the failure:

```
AssertionError: (/Users/wichert/Development/chameleon/src/chameleon/tests/inputs/092-char-suffix.pt) - 
Expected:
    <html>
    <body>
        <tr>
            <td class="tavara_col1"><input name="1-koodi" value="456"></td>
            <td class="tavara_col2"><input name="1-nimi" value="DEF"></td>
            <td class="tavara_col3"><input name="1-hinta" value="32.0"></td>
            <td class="tavara_col4"><input name="1-maara" value="23"></td>
            <td class="tavara_col5"><input name="1-A" type="checkbox" checked></td>
            <td class="tavara_col6"><input name="1-T" type="checkbox" checked></td>
        </tr>
        <tr>
            <td class="tavara_col1"><input name="1-koodi" value="456"></td>
            <td class="tavara_col2"><input name="1-nimi" value="DEF"></td>
            <td class="tavara_col3"><input name="1-hinta" value="32.0"></td>
            <td class="tavara_col4"><input name="1-maara" value="23"></td>
            <td class="tavara_col5"><input name="1-A" type="checkbox" checked></td>
            <td class="tavara_col6"><input name="1-T" type="checkbox" checked></td>
        </tr>
      </body>
    </html>
Got:
    <html>
    <body>
        <tr>
            <td class="tavara_col1"><input name="1-koodi" value="456"></td>
            <td class="tavara_col2"><input name="1-nimi" value="DEF"></td>
            <td class="tavara_col3"><input name="1-hinta" value="32.0"></td>
            <td class="tavara_col4"><input name="1-maara" value="23"></td>
            <td class="tavara_col5"><input name="${tavara.id}-A" type="checkbox" checked></td>
            <td class="tavara_col6"><input name="${tavara.id}-T" type="checkbox" checked></td>
        </tr>
        <tr>
            <td class="tavara_col1"><input name="1-koodi" value="456"></td>
            <td class="tavara_col2"><input name="1-nimi" value="DEF"></td>
            <td class="tavara_col3"><input name="1-hinta" value="32.0"></td>
            <td class="tavara_col4"><input name="1-maara" value="23"></td>
            <td class="tavara_col5"><input name="${tavara.id}-A" type="checkbox" checked></td>
            <td class="tavara_col6"><input name="${tavara.id}-T" type="checkbox" checked></td>
        </tr>
      </body>
    </html>
```