[PATCH 2 of 3 V3] localrepo: make it possible to reuse manifest when commiting context

[Mateusz Kwapich]

# HG changeset patch
# User Mateusz Kwapich <mitrandir at fb.com>
# Date 1479409155 28800
#      Thu Nov 17 10:59:15 2016 -0800
# Node ID 4a0824bead3ba5980bd8528937fba5f7bb31ba9f
# Parent  7dfd4c184ee087f2c05e1bdae8a10ccefbff7a92
localrepo: make it possible to reuse manifest when commiting context

This makes the commit function understand the context that's reusing manifest.

diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -1695,7 +1695,11 @@ class localrepository(object):
             tr = self.transaction("commit")
             trp = weakref.proxy(tr)
 
-            if ctx.files():
+            if ctx.manifestnode():
+                # reuse an existing manifest revision
+                mn = ctx.manifestnode()
+                files = ctx.files()
+            elif ctx.files():
                 m1ctx = p1.manifestctx()
                 m2ctx = p2.manifestctx()
                 mctx = m1ctx.copy()