bin/bitbake:

bin/bitbake:
    * check if a package's task is already complete _before_
      calling the functions to try to build it.
    * don't bother trying to build a package's deps if the package has
      already been built.
    * cache the information about the 'perhaps you should define
      PREFERRED_PROVIDER_blah' messages so that the user only sees one
      for each provider.