DOC: fix conflicting ewma documentation
Merge pull request #4499 from Komnomnomnom/moments-doc-

DOC: fix conflicting ewma documentation
BLD: test_perf, bring back pickle-compare code clobbered in 244d56751
BLD: test_perf, revert s/save/to_pickle change, warn the unwary
Merge pull request #4644 from y-p/PR_test_perf_fixes

test_perf fixes, restore clobbered pickle compare cmdargs, restore back_compat
PERF: optimize __getitem__ in DataFrame for columns lookup
Merge pull request #4639 from jreback/gi_perf

PERF: optimize __getitem__ in DataFrame for columns lookup