BUG: DataFrame constructor should not promote complex64 dtypes (GH10952)
Addresses [GH10952](https://github.com/pydata/pandas/issues/10952).

When passing an array with complex64 dtype to the DataFrame constructor, that array will no longer be automatically promoted to the complex128 dtype (different complex dtypes are now allowed).

very simple! nice!
 merged via https://github.com/pydata/pandas/commit/b5b06cf7615a8c8f956aa80ef023a3748e786df5

tip: to avoid merge conflicts in the whatsnew, put the entry not at the end, that's why I leave blank spaces in the Bug fixes (though this is a slight api change).
 Thanks! I'll remember to leave spaces in the file next time.
