evolve: extract "update" code into its own function This patch moves the code to a function which handles the case when wdir parent is obsolete and evolve will just update to its successor. And extraction of this to a function will also help us to fix the issue5881.

# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)