Styler class fails to render numeric columns when 0 not in columns
The `core.style.Styler._translate` method uses `__getitem__` indexing when working with numerical cell locations (https://github.com/pydata/pandas/blob/master/pandas/core/style.py#L240). When using numeric dataframe columns the location based index causes confusion with the column name index, causing an error. 

``` python
df = pd.DataFrame({i: range(10) for i in range(1,10)})
df.style._translate()
```

The expected behaviour should be to always use location based indexing. Changing [line 240](https://github.com/pydata/pandas/blob/master/pandas/core/style.py#L240) to:

``` python
    "value": self.data.iloc[r].iloc[c],
```

Fixes the error.

I do currently have a PR to fix this but wanted to file the bug report first. 
##### Error code

```
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
/usr/local/lib/python3.5/site-packages/IPython/core/formatters.py in __call__(self, obj)
    339             method = _safe_get_formatter_method(obj, self.print_method)
    340             if method is not None:
--> 341                 return method()
    342             return None
    343         else:

/usr/local/lib/python3.5/site-packages/pandas/core/style.py in _repr_html_(self)
    158         Hooks into Jupyter notebook rich display system.
    159         '''
--> 160         return self.render()
    161 
    162     def _translate(self):

/usr/local/lib/python3.5/site-packages/pandas/core/style.py in render(self)
    259         """
    260         self._compute()
--> 261         d = self._translate()
    262         # filter out empty styles, every cell will have a class
    263         # but the list of props may just be [['', '']].

/usr/local/lib/python3.5/site-packages/pandas/core/style.py in _translate(self)
    220                 cs = [DATA_CLASS, "row%s" % r, "col%s" % c]
    221                 cs.extend(cell_context.get("data", {}).get(r, {}).get(c, []))
--> 222                 row_es.append({"type": "td", "value": self.data.iloc[r][c],
    223                                "class": " ".join(cs), "id": "_".join(cs[1:])})
    224                 props = []

/usr/local/lib/python3.5/site-packages/pandas/core/series.py in __getitem__(self, key)
    555     def __getitem__(self, key):
    556         try:
--> 557             result = self.index.get_value(self, key)
    558 
    559             if not np.isscalar(result):

/usr/local/lib/python3.5/site-packages/pandas/core/index.py in get_value(self, series, key)
   1788 
   1789         try:
-> 1790             return self._engine.get_value(s, k)
   1791         except KeyError as e1:
   1792             if len(self) > 0 and self.inferred_type in ['integer','boolean']:

pandas/index.pyx in pandas.index.IndexEngine.get_value (pandas/index.c:3204)()

pandas/index.pyx in pandas.index.IndexEngine.get_value (pandas/index.c:2903)()

pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:3843)()

pandas/hashtable.pyx in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:6525)()

pandas/hashtable.pyx in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:6463)()

KeyError: 0
```
## INSTALLED VERSIONS

commit: None
python: 3.5.1.final.0
python-bits: 64
OS: Darwin
OS-release: 15.3.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.17.1
nose: 1.3.7
pip: 7.1.2
setuptools: 19.4
Cython: None
numpy: 1.10.4
scipy: 0.16.0
statsmodels: None
IPython: 4.0.3
sphinx: 1.3.1
patsy: None
dateutil: 2.4.2
pytz: 2015.7
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.4.3
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
Jinja2: 2.8
