DataFrame with 'list of dicts' behaviour proposal
Sketch of proposed behaviour... make 'list of dicts' create a (potentially) 'ragged' array, with autoguessed column names, and sensible default values, when the keys don't exist in all dicts.

Current behaviour:

In [215]: pandas.DataFrame([dict(a=1),dict(a=2)],columns=['a'])
Out[215]: 
   a  
0  {'a': 1}
1  {'a': 2}

(I happen to find this very surprising/useless behaviour!)

(one) Proposed behaviour...

> > > print DataFrame2([dict(a=1,c=1,d=True),dict(b=2,c='abc')])
> > >    a    c    d  
> > > 0  1    1    True
> > > 1  NaN  abc  NaN 

I have a straw implementation at:  https://gist.github.com/1511578

(there is a lot to comment on!... should it use the set of keys?  Do we need more args?  Documentation?  Is this just a recipe?)
