CI: use current versions for excel / dateutil / pytz on 3.4 build
Merge pull request #7170 from jreback/new

CI: use current versions for excel / dateutil / pytz on 3.4 build
CLN: Deprecation of assert_

#7131: Run s/self.assert_(/self.assertTrue( on remaining instances I can find. These were the multi-line expressions, and I tried to retain the formatting of the expressions
CLN: Deprecation of assert_

Fix formatting of one multi-line assertion, from assert_ --> assertTrue cleanup
Merge pull request #7172 from bwignall/issue7131_assert_

CLN: Deprecation of assert_
BUG: fix isnull for 0d object arrays
Merge pull request #7176 from shoyer/isnull-0d-object-array

BUG: fix isnull for 0d object arrays
add tests for nanops
implement additional tests for groupby apply methods
simplify groupby's std method
add sem to nanops
add sem to aggregate methods
add sem to groupby
add sem to docs