modeling is broken for multi param sets?

I rebased astropy this morning and I started getting errors when trying to use some of the models with multiple parameter sets. Example:

    from astropy.modeling import models
    m = models.Const1DModel([1,2])
    y = m(1)
```
ERROR: ValueError: total size of new array must be unchanged [astropy.modeling.core]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/lim/python33/lib/python3.3/site-packages/astropy-0.3.dev6223-py3.3-linux-x86_64.egg/astropy/modeling/core.py", line 106, in wrapped_call
    result = func(self, *converted)
  File "/home/lim/python33/lib/python3.3/site-packages/astropy-0.3.dev6223-py3.3-linux-x86_64.egg/astropy/modeling/core.py", line 971, in __call__
    return self.eval(x, *self.param_sets)
  File "/home/lim/python33/lib/python3.3/site-packages/astropy-0.3.dev6223-py3.3-linux-x86_64.egg/astropy/modeling/core.py", line 232, in param_sets
    psets.shape = (len(self.param_names), self.param_dim)
ValueError: total size of new array must be unchanged
```

After some investigation, I found out that unless `param_dim` is explicitly set as in `Gaussian1DModel`, it will always be 1.