BUG: subclassed .align returns normal DataFrame

[sinhrks]

• closes DataFrame align() on a subclassed DataFrame does not invoke _constructor() for the subclassed DataFrame #12983
• tests added / passed
• passes git diff upstream/master | flake8 --diff
• whatsnew entry

Also fixed a bug which Series.align(DataFrame) raises AttributeError.

pd.Series([1, 2], index=['a', 'b']).align(pd.DataFrame([1, 2], index=['a', 'c']))
# AttributeError: 'Series' object has no attribute 'columns'

[codecov-io]

Current coverage is 84.07%

Merging #13037 into master will increase coverage by +<.01%

@@             master     #13037   diff @@
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  Files           136        136          
  Lines         49994      49999     +5   
  Methods           0          0          
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+ Hits          42028      42033     +5   
  Misses         7966       7966          
  Partials          0          0          

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[jreback]

thanks @sinhrks