sieve vacation draft

Hi.  This is a second stab at a vacation extension.  Please take a look at it.

Lowlights: I'm not satisfied with section 4.  If someone can suggest
good wording for both the base document and section 4 in this document
that makes action interactions clear, I'd really appreciate it.
Otherwise the interactions are going to be very badly defined and
implemented.

Tim

-- 
Tim Showalter <tjs+(_at_)andrew(_dot_)cmu(_dot_)edu>