Merge pull request #4738 from jreback/bool_single

API: allow single element boolean Series to improve on numpy behavior( related GH4657)
Merge pull request #5050 from jreback/dir

API: provide __dir__ method (and local context) for tab completion / remove ipython completers code
BUG: Make sure series-series boolean comparions are label based (GH4947)
ENH: Series lhs, scalar rhs bool comparison support