Core

To cover the case of multivalue-checkboxes in TYPO3 Core Fluid CheckboxViewhelper I have applied implementation of the FLOW.Fluid CheckboxViewhelper.
I don't know whether it is enough but it looks like all to do is to change the method signature from

public function render($checked = NULL)

to

public function render($checked = NULL, $multiple = NULL)

and remove the @todo annotation in the representing if condition:

elseif (($multiple = FALSE) === TRUE) {
    // @todo: implement correct as in Flow.Fluid
    $nameAttribute .= '[]';
}

to

elseif ($multiple === TRUE) {
    $nameAttribute .= '[]';
}