[Seaside] Checkbox attributes

[C. David Shaffer]

The use of hidden fields around checkboxes in 
WAHtmlRendered>>checkboxWithValue:callback:confuses attribute settings.  
That is, if you set attributes then invoke that method, your attributes 
are placed on a hidden field and not the checkbox itself.  I can't 
imagine a situation in which that is what you wanted.  I propose 
changing that method to something like:

checkboxWithValue: aBoolean callback: callbackBlock
    | value originalAttributes |
    value _ ValueHolder new.
    originalAttributes _ attributeBuffer.
    attributeBuffer _ nil.
    self
        hiddenInputWithCallback: [value contents: false].
    attributeBuffer _ originalAttributes.
    self attributeAt: 'checked' put: aBoolean.
    self
        valueInputOfType: 'checkbox'
        value: 'true'
        callback: [value contents: true].
    callbackBlock fixTemps.
    self
        hiddenInputWithCallback: [callbackBlock value: value contents]

I'm sure Avi will give something better but I hate complaining without 
supplying an attempt at a solution :-)

David