Import BatchRowUpdate classes from Echo

Import BatchRowUpdate classes from Echo

This is a set of classes written for Echo to simplify writing
maintenance scripts that iterate over an entire table and update
some of those rows.

This has shown to be reusable elsewhere, especially the BatchRowIterator
class and will be useful to have generally avilable in core. The Echo
classes are all prefixed with the Echo name so there wont be any
conflict is both are installed.

Change-Id: I64c1751106caf34f41af799dbaf8794115537f06