patch from https://bugs.launchpad.net/zc.buildout/+bug/144228.

src/zc/buildout/buildout.py

@@ -787,9 +787,7 @@ class Buildout(UserDict.DictMixin):
             if not f:
                 continue
             f = self._buildout_path(f)
-            if os.path.isdir(f):
-                rmtree(f)
-            elif os.path.isfile(f):
+            if os.path.isfile(f) or os.path.islink(f):
                 try:
                     os.remove(f)
                 except OSError:
@@ -804,6 +802,8 @@ class Buildout(UserDict.DictMixin):
                         # and, of course, it's in use. Leave it.
                         ):
                         raise
+            elif os.path.isdir(f):
+                rmtree(f)
 
     def _install(self, part):
         options = self[part]