update zeo buildout to use an absolute path for blob-storage in ord…

…er to avoid [http://thread.gmane.org/gmane.comp.web.zope.plone.devel/23534 weird setup issues]

svn path=/buildouts/plone-coredev/branches/4.0/; revision=34327

zeo.cfg

@@ -4,7 +4,7 @@ parts += zeo
 
 [zeo]
 recipe = plone.recipe.zeoserver
-blob-storage = var/blobstorage
+blob-storage = ${buildout:directory}/var/blobstorage
 zeo-address = 8100
 
 [instance]