Cannot print DataFrame with non-ascii column names in ipython 3.0.0
``` python
import pandas
df = pandas.DataFrame({u'превед':[1,2,3]})
df
```

I get:

```
UnicodeDecodeError                        Traceback (most recent call last)
<ipython-input-1-114199e6a3fa> in <module>()
      3 print pandas.__version__
      4 df = pandas.DataFrame({u'превед':[1,2,3]})
----> 5 df

/home/gutman/trash/ipython/IPython/core/displayhook.pyc in __call__(self, result)
    242             self.update_user_ns(result)
    243             self.log_output(format_dict)
--> 244             self.finish_displayhook()
    245 
    246     def flush(self):

/home/gutman/trash/ipython/IPython/kernel/zmq/displayhook.pyc in finish_displayhook(self)
     66         sys.stdout.flush()
     67         sys.stderr.flush()
---> 68         self.session.send(self.pub_socket, self.msg, ident=self.topic)
     69         self.msg = None
     70 

/home/gutman/trash/ipython/IPython/kernel/zmq/session.pyc in send(self, stream, msg_or_type, content, parent, ident, buffers, track, header, metadata)
    647         if self.adapt_version:
    648             msg = adapt(msg, self.adapt_version)
--> 649         to_send = self.serialize(msg, ident)
    650         to_send.extend(buffers)
    651         longest = max([ len(s) for s in to_send ])

/home/gutman/trash/ipython/IPython/kernel/zmq/session.pyc in serialize(self, msg, ident)
    551             content = self.none
    552         elif isinstance(content, dict):
--> 553             content = self.pack(content)
    554         elif isinstance(content, bytes):
    555             # content is already packed, as in a relayed message

/home/gutman/trash/ipython/IPython/kernel/zmq/session.pyc in <lambda>(obj)
     83 # disallow nan, because it's not actually valid JSON
     84 json_packer = lambda obj: jsonapi.dumps(obj, default=date_default,
---> 85     ensure_ascii=False, allow_nan=False,
     86 )
     87 json_unpacker = lambda s: jsonapi.loads(s)

/usr/local/lib/python2.7/dist-packages/zmq/utils/jsonapi.pyc in dumps(o, **kwargs)
     38         kwargs['separators'] = (',', ':')
     39 
---> 40     s = jsonmod.dumps(o, **kwargs)
     41 
     42     if isinstance(s, unicode):

/usr/lib/python2.7/json/__init__.pyc in dumps(obj, skipkeys, ensure_ascii, check_circular, allow_nan, cls, indent, separators, encoding, default, **kw)
    236         check_circular=check_circular, allow_nan=allow_nan, indent=indent,
    237         separators=separators, encoding=encoding, default=default,
--> 238         **kw).encode(obj)
    239 
    240 

/usr/lib/python2.7/json/encoder.pyc in encode(self, o)
    202         if not isinstance(chunks, (list, tuple)):
    203             chunks = list(chunks)
--> 204         return ''.join(chunks)
    205 
    206     def iterencode(self, o, _one_shot=False):

UnicodeDecodeError: 'ascii' codec can't decode byte 0xd0 in position 4: ordinal not in range(128)
```
