Replace allBindingsAccessor function with allBindings object with get and has methods (function interface is maintained for backwards compatibility only).
Rename wrapValue/unwrapValue to makeValueAccessor/evaluateValueAccessor to avoid confusion with ko.utils.unwrapObservable
Merge pull request #932 from SteveSanderson/indi-binding-support-allBindingsAccessor

Independent binding support: accessing sibling bindings (allBindingsAccessor)