The new slapos.libnetworkcache depends on M2Crypto.

Well, according to the developing done in:
  - https://git.erp5.org/gitweb/slapos.libnetworkcache.git/shortlog/refs/heads/signature?js=1

It is required to build M2Crypto, otherwise it is not possible to use
the signature feature provided by slapos.libnetworkcache.

component/slapos/buildout.cfg

 [buildout]
+# path to slapos.libnetworkcache branch signature
+# git clone https://git.erp5.org/repos/slapos.libnetworkcache.git
+# cd slapos.libnetworkcache && git checkout signature
+#develop = ....slapos.libnetworkcache-signature
 extends =
   ../../stack/shacache-client.cfg
   ../m2crypto/buildout.cfg
   ../lxml-python/buildout.cfg
   ../python-2.7/buildout.cfg
+  ../m2crypto/buildout.cfg
 
 parts =
+  M2Crypto
   slapos
 
 find-links =
@@ -30,6 +36,9 @@ allowed-eggs-from-site-packages =
 [lxml-python]
 python = python2.7
 
+[slapos.libnetworkcache]
+python = python2.7
+
 [M2Crypto]
 python = python2.7
 
@@ -37,7 +46,7 @@ python = python2.7
 recipe = z3c.recipe.scripts
 python = python2.7
 eggs =
-  ${M2Crypto:egg}
+  M2Crypto
   slapos.libnetworkcache
   zc.buildout
   ${lxml-python:egg}
@@ -69,7 +78,7 @@ meld3 = 0.6.7
 netaddr = 0.7.5
 setuptools = 0.6c12dev-r88846
 slapos.core = 0.12
-slapos.libnetworkcache = 0.4
+slapos.libnetworkcache =
 xml-marshaller = 0.9.7
 z3c.recipe.scripts = 1.0.1
 zc.recipe.egg = 1.3.2