Marks given ``FileNode`` objects as *to be committed*.

        :raises ``NodeAlreadyExistsError``: if node with same path exists at
          latest changeset
        :raises ``NodeAlreadyAddedError``: if node with same path is already
          marked as *added*

def add(self, *filenodes):
        """
        Marks given ``FileNode`` objects as *to be committed*.

        :raises ``NodeAlreadyExistsError``: if node with same path exists at
          latest changeset
        :raises ``NodeAlreadyAddedError``: if node with same path is already
          marked as *added*
        """
        # Check if not already marked as *added* first
        for node in filenodes:
            if node.path in (n.path for n in self.added):
                raise NodeAlreadyAddedError("Such FileNode %s is already "
                    "marked for addition" % node.path)
        for node in filenodes:
            self.added.append(node)