BUG: DataFrame.round() drops column index name #11986
Fixes #11986. Used the same reconstruction method as `DataFrame.isin()` to ensure that column names are kept through rounding. Works with `np.round` as well.

Pretty minor fix -- does this need a release note or anything else?

tests!
 +tests for `np.round` and `DataFrame.round` to ensure that the column names are preserved and that the rounding isn't otherwise affected.
 Better like this?
 yes although I wouldn't change it back to None (just change any expected after this)
 can u update the series test as well (add a name)
it should work already
 I'd put the new test in the middle of the rounding tests, so there would have been a lot of expected frames to fix without resetting the name. I've moved it to the bottom now, and added tests to ensure that naming the columns doesn't mess up `Series.round` or the name of a selected `Series` after a `DataFrame.round`.
 pls add an entry in whatsnew for this bug fix.
 gr8. ping when green.
 Green. Thanks for the help with this, @jreback 
 merged via https://github.com/pydata/pandas/commit/9b5c052b0807e4990dd5a8fe39238153c2ec9632

thanks!
