Add how kwarg to rolling_* functions [fix #6297]
API: remove the copy kw from .xs to prevent accidental / confusing setting (GH6894)
BUG: legend behaves inconsistently when plotting to the same axes repeatedly
Merge pull request #6919 from jreback/xs_copy

API: remove the copy kw from .xs to prevent an expectation of a view (which may not be possible)
Merge pull request #6845 from jsexauer/fix6297_pr

BUG/ENH: Add how kwarg to rolling_* functions [fix #6297]
Merge pull request #6678 from sinhrks/legend_pr

BUG: legend behaves inconsistently when plotting to the same axes
API: Stop modifying SQL column and names, and warn when pertinent.
BUG/INT: Internal tests for patching __finalize__ / bug in merge not finalizing (GH 6923)
Merge pull request #6924 from jreback/finalize

BUG/INT: Internal tests for patching __finalize__ / bug in merge not finalizing (GH6923)
Merge pull request #6902 from danielballan/remove-safe-col-names

API: Stop modifying SQL column and names, and warn when pertinent.
ENH: Added CustomBusinessMonth offset.
API: align Panel.shift API with generic
change pct_change back to a kwarg
Merge pull request #6928 from TomAugspurger/panel_shift_kwarg

API/DEPR: Match Panel.shift()'s signature to generic
Deprecate order kwarg in factorize
BUG/INT: Internal tests for patching __finalize__ / bug in concat not finalizing (GH 6927)
Merge pull request #6866 from bjonen/cbm

Custom Business Month
Merge pull request #6931 from jreback/finalize2

BUG/INT: Internal tests for patching __finalize__ / bug in concat not finalizing (GH6927)
ENH: Use Welford's method in stats.moments.rolling_var

This PR implements a modified version of Welford's method to compute
the rolling variance. Instead of keeping track of the sum and sum of
the squares of the items in the window, it tracks the mean and the sum
of squared differences from the mean. This turns out to be (much) more
numerically stable.

The formulas to update these two variables when adding or removing an
item from the sequence are well known, see e.g.

http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance

The formulas used when both adding one and removing one item I have
not seen explicitly worked out anywhere, but are not too hard to come
up with if you put pen to (a lot of) paper.
Merge pull request #6930 from TomAugspurger/factorize-kwarg

API/DEPR: Deprecate order kwarg in factorize