Change tree pruning algorithm

The first merge we see in Factory determines if we keep the devel
commits in the factory chain or cut that branch.

lib/importer.py

@@ -1,4 +1,3 @@
-import functools
 import logging
 import os
 import xml.etree.ElementTree as ET
@@ -15,6 +14,7 @@ from lib.proxy_sha256 import ProxySHA256, md5, sha256
 from lib.tree_builder import AbstractWalker, TreeBuilder, TreeNode
 from lib.user import User
 
+
 class Importer:
     def __init__(self, projects, package, repodir):
         # The idea is to create each commit in order, and draw the