ERR: frame construction with all scalars doesn't raise when columns are provided

[jreback]

xref #9456

[39] should raise.

In [38]: pd.DataFrame({'a':0.1})
ValueError: If using all scalar values, you must pass an index

In [39]: pd.DataFrame({'a':0.1}, columns=['b'])
Out[39]:
Empty DataFrame
Columns: [b]
Index: []

[ajcr]

At the pandas sprint - I can have a look at this now...