BUG: ujson labels are encoded twice
Merge pull request #4593 from Komnomnomnom/ujson-slash-happy

BUG: ujson labels are encoded twice
Merge pull request #4610 from jreback/series_reindex

CLN: refactor Series.reindex to core/generic
ENH: Keep original traceback in DataFrame.apply

When "raise <exception instance>" is used inside a try/except block, the
original stacktrace (containing the code path that raised the original
exception).  This makes debugging difficult since all we know is that an error
occured when `frame._apply_standard` attempted to call the provided function.
Preserve the original stacktrace by using "raise" instead of "raise <exception
instance>".  This facilitates debugginb by allowing us to see where (in the
provided callable) the exception occured.

Added mention of this change in release notes
Merge pull request #4549 from bburan-galenea/bburan-galenea/apply_exception_traceback

ENH/API: Keep original traceback in DataFrame.apply
BUG: Fix boolean comparison with a DataFrame on the lhs, and a list/tuple on the rhs GH4576