BUG: algorithms._count_generic?
`algorithms._count_generic` returns a `Series` built from `counts`, which isn't defined:

```
def _count_generic(values, table_type, type_caster):
    from pandas.core.series import Series

    values = type_caster(values)
    table = table_type(min(len(values), 1000000))
    uniques, labels = table.factorize(values)

    return Series(counts, index=uniques)
```

but this function doesn't seem to be used anywhere.  The only reference I can find is in `algorithms.count`, or what would be `algorithms.count`, but that's commented out:

```
# def count(values, uniques=None):
#     f = lambda htype, caster: _count_generic(values, htype, caster)

#     if uniques is not None:
#         raise NotImplementedError
#     else:
#         return _hashtable_algo(f, values.dtype)
```
