title: Pandas json_normalize produces confusing `KeyError` message?
body: <p>I'm trying to convert a nested JSON to a Pandas dataframe. I've been using <code>json_normalize</code> with success until I came across a certain JSON. I've made a smaller version of it to recreate the problem.</p>
  
  <pre><code>from pandas.io.json import json_normalize
  
  json=[{"events": [{"schedule": {"date": "2015-08-27",
       "location": {"building": "BDC", "floor": 5},
       "ID": 815},
      "group": "A"},
     {"schedule": {"date": "2015-08-27",
       "location": {"building": "BDC", "floor": 5},
   "ID": 816},
  "group": "A"}]}]
  </code></pre>
  
  <p>I then run:</p>
  
  <pre><code>json_normalize(json[0],'events',[['schedule','date'],['schedule','location','building'],['schedule','location','floor']])
  </code></pre>
  
  <p>Expecting to see something like this:</p>
  
  <pre><code>ID      group   schedule.date   schedule.location.building schedule.location.floor  
  '815'   'A'     '2015-08-27'            'BDC'                       5
  '816'   'A'     '2015-08-27'            'BDC'                       5
  </code></pre>
  
  <p>But instead I get this error:</p>
  
  <pre><code>In [2]: json_normalize(json[0],'events',[['schedule','date'],['schedule','location','building'],['schedule','location','floor']])
  ---------------------------------------------------------------------------
  KeyError                                  Traceback (most recent call last)
  &lt;ipython-input-2-b588a9e3ef1d&gt; in &lt;module&gt;()
  ----&gt; 1 json_normalize(json[0],'events',[['schedule','date'],['schedule','location','building'],['schedule','location','floor']])
  
  /Users/logan/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/io/json.pyc in json_normalize(data, record_path, meta, meta_prefix, record_prefix)
      739                 records.extend(recs)
      740
  --&gt; 741     _recursive_extract(data, record_path, {}, level=0)
      742
      743     result = DataFrame(records)
  
  /Users/logan/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/io/json.pyc in _recursive_extract(data, path, seen_meta, level)
      734                         meta_val = seen_meta[key]
      735                     else:
  --&gt; 736                         meta_val = _pull_field(obj, val[level:])
      737                     meta_vals[key].append(meta_val)
      738
  
  /Users/logan/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/io/json.pyc in _pull_field(js, spec)
      674         if isinstance(spec, list):
      675             for field in spec:
  --&gt; 676                 result = result[field]
      677         else:
      678             result = result[spec]
  
  KeyError: 'schedule'
  </code></pre>