Extract prereqs for all the phases, rather than just the ones I know about.
Allow stats command to work on a specific stack.
Update change log.
Stop pulling developer prereqs by default.

You can still get them by adding the --with-development-prereqs
option to either the "add" or "pull" command.

I implemented this by adding another filter on the
PrerequisiteWalker.  Notice that it now takes multiple
filters.