Quantity with units returns True for __eq__ with plain numpy array 

Consider this:
```
In [10]: 2.1*pq.m == np.array(2.1)
Out[10]: True
```
I would have expected it to return True only if the Quantity instance was dimensionless.
What do others think?

EDIT:
since the numbers (arrays) cannot be added to each other, I think it really should be an error:
```
>>> 3*pq.m + 3
ValueError ...
```