[PATCH 1 of 4 evolve-ext] metaedit: add a helper function for just metadata rewrites

[Mateusz Kwapich]

# HG changeset patch
# User Mateusz Kwapich <mitrandir at fb.com>
# Date 1479324110 0
#      Wed Nov 16 19:21:50 2016 +0000
# Branch stable
# Node ID 744c6acd84edf73ffdf505b9673b0383db727a0e
# Parent  727c7211c810d304ebf92b32db7ecf697ce46ac6
metaedit: add a helper function for just metadata rewrites

It will be used by metaedit.

diff --git a/hgext/evolve.py b/hgext/evolve.py
--- a/hgext/evolve.py
+++ b/hgext/evolve.py
@@ -907,6 +907,13 @@ def rewrite(repo, old, updates, head, ne
     finally:
         lockmod.release(tr, lock, wlock)
 
+def metarewrite(repo, old, newbases, commitopts):
+    '''Like rewrite but affects only the changeset metadata.'''
+    # TODO: reuse the manifest for speed
+    newid, created = rewrite(repo, old, [old], old, newbases,
+                             commitopts=commitopts)
+    return newid, created
+
 class MergeFailure(error.Abort):
     pass