BUG: frame creation with multi-index and tuples in dict
```
In [1]: import pandas;import numpy;import datetime;
In [2]: v = datetime.date.today()
In [3]: pandas.DataFrame({v : pandas.Series(range(3),index=range(3))}, columns=[v])
Out[3]:
   2015-08-20
0           0
1           1
2           2
In [4]: v = v, v
In [5]: pandas.DataFrame({v : pandas.Series(range(3),index=range(3))}, columns=[v])
Out[5]:
  (2015-08-20, 2015-08-20)
0                      NaN
1                      NaN
2                      NaN
```
