[PATCH 3 of 9 V2] amend: use dirstateguard instead of dirstate.invalidate

[FUJIWARA Katsunori]

# HG changeset patch
# User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
# Date 1430582197 -32400
#      Sun May 03 00:56:37 2015 +0900
# Node ID 80a0f16dcf3cbce2ea50db0d6408f848bc1a75e2
# Parent  ea0832f5425148072ca048997fb322615e90e805
amend: use dirstateguard instead of dirstate.invalidate

Before this patch, "cmdutil.amend()" uses "dirstate.invalidate()" as a
kind of "restore .hg/dirstate to the original status" at failure.

But it just discards changes in memory, and doesn't actually restore
".hg/dirstate". Then, it can't work as expected, if "dirstate.write()"
is executed while processing.

This patch uses "dirstateguard" instead of "dirstate.invalidate()" to
restore ".hg/dirstate" at failure even if "dirstate.write()" is
executed before failure.

This is a part of preparations to fix the issue that recent (in
memory) dirstate isn't visible to external process (e.g. "precommit"
hook).

diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -2464,9 +2464,10 @@
     ui.note(_('amending changeset %s\n') % old)
     base = old.p1()
 
-    wlock = lock = newid = None
+    wlock = dsguard = lock = newid = None
     try:
         wlock = repo.wlock()
+        dsguard = dirstateguard(repo, 'amend')
         lock = repo.lock()
         tr = repo.transaction('amend')
         try:
@@ -2637,6 +2638,7 @@
             tr.close()
         finally:
             tr.release()
+        dsguard.close()
         if not createmarkers and newid != old.node():
             # Strip the intermediate commit (if there was one) and the amended
             # commit
@@ -2645,9 +2647,7 @@
             ui.note(_('stripping amended changeset %s\n') % old)
             repair.strip(ui, repo, old.node(), topic='amend-backup')
     finally:
-        if newid is None:
-            repo.dirstate.invalidate()
-        lockmod.release(lock, wlock)
+        lockmod.release(lock, dsguard, wlock)
     return newid
 
 def commiteditor(repo, ctx, subs, editform=''):