Incorrect type when odo-ing to a list from the SQL backend wrapped in Data

``` sql
create table t (a integer);
insert into t values (1), (2), (3);
```

``` python
In [10]: from blaze import Data

In [11]: from odo import odo, resource

In [12]: d = Data('postgresql://localhost::t')

In [13]: d.a
Out[13]:
a
0 1
1 2
2 3

In [14]: odo(d.a, list)
Out[14]: [1.0, 2.0, 3.0]

In [15]: d.a.dshape
Out[15]: dshape("var * ?int32")
```