export: enable formatter support (API) This change is basically the same as "hg cat". A formatter object is created by caller. .. api:: ``cmdutil.export()`` takes a formatter as an argument.

export: extract function to write patch to file object (API) This is common use case of cmdutil.export(), and we wouldn't want to handle formatter thingy everywhere. .. api:: The ``fp`` argument is removed from ``cmdutil.export()``. Use ``cmdutil.exportfile()`` instead.