[PATCH 3 of 4] phase: document the replace method

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1434409584 25200
#      Mon Jun 15 16:06:24 2015 -0700
# Node ID 18cc713258b6240bc0543aa5ceb537a80a8a85e5
# Parent  2acfb673a817808b6993ae5e84466a42d4cd63b7
phase: document the replace method

This is a minor documentation update to answer a co-worker question.

diff --git a/mercurial/phases.py b/mercurial/phases.py
--- a/mercurial/phases.py
+++ b/mercurial/phases.py
@@ -169,10 +169,11 @@ class phasecache(object):
         ph._phaserevs = self._phaserevs
         ph._phasesets = self._phasesets
         return ph
 
     def replace(self, phcache):
+        """replace all values in 'self' with content of phcache"""
         for a in 'phaseroots dirty opener _phaserevs _phasesets'.split():
             setattr(self, a, getattr(phcache, a))
 
     def _getphaserevsnative(self, repo):
         repo = repo.unfiltered()