Work around circular imports inside slapos.buildout

slapos/recipe/downloadunpacked.py

@@ -31,7 +31,6 @@ import tarfile
 import tempfile
 from hashlib import md5
 from setuptools import archive_util
-from zc.buildout import download
 from . import is_true, EnvironMixin, Shared
 from . import make_read_only_recursively # for slapos.recipe.cmmi
 
@@ -60,6 +59,9 @@ class Recipe(EnvironMixin):
     return self._shared.install(self._install)
 
   def _install(self):
+    # WKRD: do not import at module-level because of circular imports
+    #       inside slapos.buildout (see networkcache support)
+    from zc.buildout import download
     location = self._shared.location
     alternate = self.options.get('alternate-url')
     path, is_temp = download.Download(self.buildout['buildout'],