[FEATURE] iterator.merge: Allow use in a chain

[neufeind]

Allow use like:
{abc -> v:iterator.merge(a: def)}

This makes it easier to join multiple arrays
in a row and also to workaround some cases
where the Fluid-parser might otherwise
have a hard time.

[NamelessCoder]

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[NamelessCoder]

Suggested method body:

    /**
     * Merges arrays/Traversables $a and $b into an array
     *
     * @param mixed $b Second array/Traversable
     * @param mixed $a First array/Traversable
     * @param boolean $useKeys If TRUE, comparison is done while also observing (and merging) the keys used in each array
     * @return array
     */
    public function render($b, $a = NULL, $useKeys = TRUE) {
        if (NULL === $a) {
            $a = $this->renderChildren();
        }
        $a = ViewHelperUtility::arrayFromArrayOrTraversableOrCSV($a, $useKeys);
        $b = ViewHelperUtility::arrayFromArrayOrTraversableOrCSV($b, $useKeys);
        $merged = GeneralUtility::array_merge_recursive_overrule($a, $b);
        return $merged;
    }

• Matches usages of v:math.* arguments a/b.
• Gets by with a single use of recursive array merging
• Is somewhat easier to follow, logic-wise

[neufeind]

Pushed new version like you suggested. I'm unsure if we should demand a or b to be set, so the original idea was to still allow to be use both :-) But I'm also fine with the current solution.
Added adjusted commit-msg. Be sure the correct one is used upon merge. (I'm not sure github picks the right one.)