Bug since switch from mechanize

[fschulze]

The behaviour related to setting radio controls has changed in some cases.

I added a test case in master...fschulze:radio-master.

I added the same one for 4.0.4 in 4.0.4...fschulze:radio-4.0.4 to show that it works correctly with mechanize.

[fschulze]

The tests in https://github.com/fschulze/zope.testbrowser/tree/radio-4.0.4 work when using the buildout and running the test script.

[mgedmin]

The failure looks like this:

**********************************************************************
File "narrative.rst", line ?, in default
Failed example:
    browser.getControl(name='radio-value-a').getControl(value='true', index=0)
Expected:
    <ItemControl name='radio-value-a' type='radio' optionValue='true' selected=False>
Got:
    <ItemControl name='radio-value-a' type='radio' optionValue='true' selected=True>
**********************************************************************

[mgedmin]

The problem here is that RadioItemControl.selected = True is translated into RadioListControl.value = RadioItemControl.value, which cannot disambiguate items with the same value.

We could be assigning to WebTest's Radio control's selectedIndex instead of value to avoid this issue.