Log Message:
Update to 1.7.10

Upstream changes:
Changes in Version 1.7-10

  o All methods that had previously been fully exported (merge.zoo,
    MATCH.default, ..., and many more) in order to be accessible to
    _all_ conceivable generics are now additionally registered as
    S3method()s for the standard generics. Exception: as.Date.* are
    still only fully exported.

  o Added a new mean() method for "zoo" objects that simply does
    mean(coredata(obj), ...).

  o Added yearmon_trans, scale_x_yearmon and scale_y_yearmon and
    yearqtr_trans, scale_x_yearqtr and scale_y_yearqtr to ggplot2 interface.

  o Removed the use of the shape and linetype aesthetic by default
    in autoplot() method.

  o Bug fix in na.fill for univariate series based on 1-column matrices
    (provided by Josh Ulrich).

  o Added [[ methods for "yearmon" and "yearqtr".

  o Constructs like time(obj)[ORDER(time(obj))] are now split up into
    two steps in the package code. If zoo is only imported but not
    loaded, R can otherwise have problems correctly dispatching to
    the new generics ORDER and MATCH.

  o as.Date() now also works for yearqtr/yearmon that are all NA
    (especially needed for format() and print() method).