[PATCH 2 of 7 🚂] transaction: document the content of `tr.backupentries`

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1415151029 0
#      Wed Nov 05 01:30:29 2014 +0000
# Node ID 579eeefd6ae1e144a2982ee914661d8f6e057a89
# Parent  589d7454fba619ad9db81552941ed5cdefebf19e
transaction: document the content of `tr.backupentries`

Now that all items are known we can document it.

diff --git a/mercurial/transaction.py b/mercurial/transaction.py
--- a/mercurial/transaction.py
+++ b/mercurial/transaction.py
@@ -81,10 +81,11 @@ class transaction(object):
         self.opener = opener
         self.after = after
         self.onclose = onclose
         self.onabort = onabort
         self.entries = []
+        # a list of ('path', 'backuppath') entries.
         self.backupentries = []
         self.map = {}
         self.backupmap = {}
         self.journal = journal
         self._queue = []