DAL cleanup project proposal

[ghudson@MIT.EDU]

I've made a few minor changes to the project proposal as I've started
working more with the code.  As a result, I've split out the principal
and policy API changes (mostly principal API changes) into a separate
section from "Simple Cleanups".

The most notable new change is that I want to make get_principal
responsible for allocating the DB entry structure.  In my experience,
it's easier to perform robust error handling when APIs allocate the
container than when the caller does.