Dot doesn't accept arrays
```
In [93]: a = rand(1,5)

In [94]: b = rand(5,1)

In [95]: A = pd.DataFrame(a)

In [96]: B = pd.DataFrame(b)

In [97]: a.dot(b)
Out[97]: array([[ 1.50425267]])

In [98]: A.dot(B)
Out[98]: 


0
0
1.504253


In [99]: a.dot(B)
Out[99]: array([[ 1.50425267]])

In [100]: A.dot(b)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
D:\Projects\moc\<ipython-input-100-2a3d67ed3e0f> in <module>()
----> 1 A.dot(b)

C:\Python27\lib\site-packages\pandas\core\frame.pyc in dot(self, other)
    722         """
    723         lvals = self.values
--> 724         rvals = other.values
    725         result = np.dot(lvals, rvals)
    726         return DataFrame(result, index=self.index, columns=other.columns)

AttributeError: 'numpy.ndarray' object has no attribute 'values'
```

I would guess replace `rvals = other.values` with

```
try:
    rvals = other.values
except AttributeError:
    pass
```

unless you specifically intended for this to fail?

Thanks,
Ludovic
