X Switch persistent to git checkout

Rst files that persistent wants to use from tests are not installed along with regular egg.

component/ZODB/buildout.cfg

@@ -70,7 +70,7 @@ depends = ${persistent:egg} ${BTrees:egg}
 egg_versions =
   # TODO update to 4.7.3 once it is released
   BTrees = 4.5.1
-  persistent = 4.6.4
+# persistent = 4.6.4
   # TODO update to 2.0.0 once NEO stops doing bytes._pack = ...
   # https://lab.nexedi.com/nexedi/slapos/commit/27f574bc
   zodbpickle = 1.0.4
@@ -162,8 +162,21 @@ recipe = zc.recipe.egg:custom
 egg = ${:_buildout_section_name_}
 setup-eggs = ${persistent:egg}
 
+# [persistent]
+# recipe = zc.recipe.egg:custom
+# egg = ${:_buildout_section_name_}
+# setup-eggs = ${python-cffi:egg}
+# ###
+
 [persistent]
-recipe = zc.recipe.egg:custom
+recipe = zc.recipe.egg:develop
 egg = ${:_buildout_section_name_}
 setup-eggs = ${python-cffi:egg}
-###
+setup = ${persistent-repository:location}
+
+[persistent-repository]
+<= _ZODB-git-repository
+location = ${buildout:parts-directory}/persistent
+repository = https://github.com/zopefoundation/persistent.git
+branch = master
+revision = 4.6.4-0-g7ed95cf