[PATCH 3 of 4 V2 mergedriver] localrepo: switch to mergestate.clean()

[Siddharth Agarwal]

# HG changeset patch
# User Siddharth Agarwal <sid0 at fb.com>
# Date 1447808672 28800
#      Tue Nov 17 17:04:32 2015 -0800
# Node ID 0177a83b0a029bc9ea5d062611448b885a409dcb
# Parent  8f3c56092848bc43af8eebbe824056898ccfa002
localrepo: switch to mergestate.clean()

See the previous patches for why we're doing this.

diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -1168,8 +1168,7 @@ class localrepository(object):
             else:
                 ui.status(_('working directory now based on '
                             'revision %d\n') % parents)
-            ms = mergemod.mergestate(self)
-            ms.reset(self['.'].node())
+            mergemod.mergestate.clean(self, self['.'].node())
 
         # TODO: if we know which new heads may result from this rollback, pass
         # them to destroy(), which will prevent the branchhead cache from being