concat on axis=1 and ignore_index=True raises TypeError
Test case:

``` python

>>> frame1 = pandas.DataFrame({"test1":["a", "b", "c"], "test2":[1,2,3], "test3": [4.5, 3.2, 1.2]})
>>> frame2 = pandas.DataFrame({"test4": [5.2, 2.2, 4.3]})
>>> pandas.concat([frame1, frame2], ignore_index=True, axis=1)

/usr/lib64/python2.7/site-packages/pandas/tools/merge.pyc in concat(objs, axis, join, join_axes, ignore_index, keys, levels, names,
    689                        keys=keys, levels=levels, names=names,
    690                        verify_integrity=verify_integrity)
--> 691     return op.get_result()
    692 
    693 

/usr/lib64/python2.7/site-packages//pandas/tools/merge.pyc in get_result(self)
    759                              columns=self.new_axes[1])
    760         else:
--> 761             new_data = self._get_concatenated_data()
    762             return self.objs[0]._from_axes(new_data, self.new_axes)
    763 

/usr/lib64/python2.7/site-packages/pandas/tools/merge.pyc in _get_concatenated_data(self)
    776             for kind in kinds:
    777                 klass_blocks = [mapping.get(kind) for mapping in blockmaps]
--> 778                 stacked_block = self._concat_blocks(klass_blocks)
    779                 new_blocks.append(stacked_block)
    780             new_data = BlockManager(new_blocks, self.new_axes)

/usr/lib64/python2.7/site-packages/pandas/tools/merge.pyc in _concat_blocks(self, blocks)
    832                 concat_items = _concat_indexes(all_items)
    833 
--> 834             return make_block(concat_values, concat_items, self.new_axes[0])
    835 
    836     def _concat_single_item(self, item):

/usr/lib64/python2.7/site-packages/pandas/core/internals.pyc in make_block(values, items, ref_items, do_integrity_check)
    287 
    288     return klass(values, items, ref_items, ndim=values.ndim,
--> 289                  do_integrity_check=do_integrity_check)
    290 
    291 # TODO: flexible with index=None and/or items=None


/usr/lib64/python2.7/site-packages/pandas/core/internals.pyc in __init__(self, values, items, ref_items, ndim, do_integrity_check)
     28         self.ndim = ndim
     29         self.items = _ensure_index(items)
---> 30         self.ref_items = _ensure_index(ref_items)
     31 
     32         if do_integrity_check:

/usr/lib64/python2.7/site-packages/pandas/core/index.pyc in _ensure_index(index_like)
   2152     if hasattr(index_like, 'name'):
   2153         return Index(index_like, name=index_like.name)
-> 2154     return Index(index_like)
   2155 
   2156 def _validate_join_method(method):

/usr/lib64/python2.7/site-packages/pandas/core/index.pyc in __new__(cls, data, dtype, copy, name)
     70         else:
     71             # other iterable of some kind

---> 72             subarr = com._asarray_tuplesafe(data, dtype=object)
     73 
     74         if lib.is_integer_array(subarr) and dtype is None:

/usr/lib64/python2.7/site-packages/pandas/core/common.pyc in _asarray_tuplesafe(values, dtype)
    493 def _asarray_tuplesafe(values, dtype=None):
    494     if not isinstance(values, (list, tuple, np.ndarray)):
--> 495         values = list(values)
    496 
    497     if isinstance(values, list) and dtype in [np.object_, object]:

TypeError: 'NoneType' object is not iterable
```

From today's git.
