[darwinbuild] darwinxref changes

[Kevin Van Vechten]

I've committed largely re-written version of darwinxref to CVS at  
proj/darwinbuild/darwinxref.

Some of the major changes include:

* NeXT-style property list support
     -- XML was illegible, but will still be supported.

* Build plists now contain a dictionary of projects, not an array.
     -- Makes syntax more consistent with semantics.
     -- Improved viewing in the Property List Editor.

* Dependency property is a dictionary of dependency types.
     -- Better organization of dependencies in the plist.

* Plug-in architecture for build plist properties.
     -- Provide future and site-specific extensibility.
     -- Potential for integration with DarwinPorts.

- Kevin