the shipping client will include the necessary generic pieces for
configuring an Exchange client (e.g. account setup) but will not
include actual Exchange client code (e.g. transport / protocol).
Also added a "sample code" implementation of Exchange for use
as a starting point for implementors. (Note, this will not ship
in Donut, it's a placeholder for working on the "framework"
aspects.)
BUG=1740621,1740626
Automated import of CL 144525
