Log Message:
math/R-xts: Update to 0.10.1

Changes:

o  'ylim' values passed to 'addSeries' and 'addPolygon' via '...' are now
   captured and honored.

o  'addPolygon' now checks for ylim of zeros, as 'addSeries' does.

o  The 'base::as.Date.numeric' method is no longer over-ridden. The exported,
   but not registered, method in zoo should prevent any change in behavior.

o  Series added to an existing plot are now given the same index values as
   the main panel. There still may be some weird behavior if the new
   data does not have observations within the timespan of the main panel data,
   but no observations on the same timestamps.

o  Existing 'par' values are now captured and reset before returning from
   plotting functions.

o  User-defined 'col' values are now honored when 'type="h"'.

o  Values passed to plotting functions are now copied from the calling
   environment. This enables plotting arguments to be objects passed
   through multiple layers of function calls.

o  Calling as.matrix() on a zero-width xts object now behaves consistently
   with zoo, and no longer throws an error.

o  Fix weird result in merge.xts() when 'fill' argument is NULL or a zero-
   length vector.

o  Fixed bug in endpoints() due to sub-second representation error via using
   integer division (%/%) with non- integer arguments.

o  endpoints() gained sub-second accuracy on Windows.

o  plot.xts() no longer errors when called on an object containing a constant
   value. It chooses ylim values +/-20% from the series value.

o  plot.xts() now places y-axis labels in the same location on the plot,
   regardless of data periodicity.

o  rbind.xts() now throws an error if passed an xts object with different
   number of observations in the index and data (e.g., zero-width).