[PATCH 3 of 9 V2] obsolete: clarify the obsstore `precursors` and `successors` mapping

[pierre-yves.david at logilab.fr]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at ens-lyon.org>
# Date 1350252694 -7200
# Node ID 79cf3c2a7ec3728e57f3c771187dd8cb9a92bfa1
# Parent  599401a6fe6f44d33656f4c69f98de2f5ecec70c
obsolete: clarify the obsstore `precursors` and `successors` mapping

A lot of people are confused by those attribute. Having a clearer docstring will
hopefully help people to understand those mapping use *markers* as value, not
node.

diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
--- a/mercurial/obsolete.py
+++ b/mercurial/obsolete.py
@@ -179,12 +179,12 @@ class marker(object):
 
 class obsstore(object):
     """Store obsolete markers
 
     Markers can be accessed with two mappings:
-    - precursors: old -> set(new)
-    - successors: new -> set(old)
+    - precursors: old -> set(marker using <old> as precursor)
+    - successors: new -> set(marker using <new> in successors)
     """
 
     def __init__(self, sopener):
         # caches for various obsolescence related cache
         self.caches = {}