MultiBox now handles sync-async

Will be required if when we do SNMP, because that one should be async.
or maybe something a bit more universal:
```python
def categorize(iterable, cat):
    for item in iterable:
        for cond, func in cat.iteritems():
            if callable(cond) and cond(item):
                func(item)
        else:
            cat.get("default", lambda item: None)(item)
``
categorize(values, {
    lambda item: isinstance(item, Async): async.append,
    lambda item: isinstance(item, Sync): sync.append,
    "default": dont_care.append
})