Fine tune optional dependency.

Fetch slapos.libnetworkcache, as will be used sooner or later.

Pin newer buildout.

buildout.cfg

@@ -20,6 +20,7 @@ eggs =
 [slapos]
 recipe = z3c.recipe.scripts
 eggs =
+  slapos.libnetworkcache
   zc.buildout
   slapos.core
   ipython
@@ -30,4 +31,4 @@ eggs =
 interpreter = python
 
 [versions]
-zc.buildout = 1.5.3-dev-SlapOS-001
+zc.buildout = 1.5.3-dev-SlapOS-004