pydata/pandas — pull request #5159 by jreback (2013-10-08 17:05:16+00:00)
Title: API/PERF: restore auto-boxing on isnull/notnull for Series (w/o copy) preserves perf gains

restore API before #5154

boxing via null/isnull is same as 0.12
(aside from now ``isnull/notnull`` are now available on ``NDFrame`` objs as well)