AI 145333: Cloned from CL 144759 by 'g4 patch'.

  Original change by joeo@abreu on 2009/04/06 19:54:13.
  Implement SDK add-ons in the build system.
  - Add an option to use the standard javadoc doclet instead
  of droiddoc, since droiddocs non-sdk templates aren't
  ready for prime time.
  - Add the notion of a stubs for a library.  It's only
  implemented for java libraries, but when we do native
  libraries in the NDK or sdk-addons, it will work there too.

Automated import of CL 145333