Loads 'file' as standalone project that has no location
        associated with it.  This is mostly useful for user-config.jam,
        which should be able to define targets, but although it has
        some location in filesystem, we do not want any build to
        happen in user's HOME, for example.

        The caller is required to never call this method twice on
        the same file.

def load_standalone(self, jamfile_module, file):
        """Loads 'file' as standalone project that has no location
        associated with it.  This is mostly useful for user-config.jam,
        which should be able to define targets, but although it has
        some location in filesystem, we do not want any build to
        happen in user's HOME, for example.

        The caller is required to never call this method twice on
        the same file.
        """
        assert isinstance(jamfile_module, basestring)
        assert isinstance(file, basestring)

        self.used_projects[jamfile_module] = []
        bjam.call("load", jamfile_module, file)
        self.load_used_projects(jamfile_module)