commands: widen wlock scope of graft for consitency while processing

Before this patch, "hg graft" executes below before acquisition of
wlock.

  - cmdutil.checkunfinished()
  - cmdutil.bailifchanged()
  - repo.dirstate.parents() via 'repo["."]'
  - unlinking '.hg/graftstate'

It may cause unintentional result, if another command runs parallelly
(see also issue4368).

This patch widens wlock scope of "hg graft" for consitency while
processing.

mercurial/commands.py

@@ -3731,7 +3731,14 b' def graft(ui, repo, *revs, **opts):'
 
     Returns 0 on successful completion.
     '''
-
+    wlock = None
+    try:
+        wlock = repo.wlock()
+        return _dograft(ui, repo, *revs, **opts)
+    finally:
+        release(wlock)
+
+def _dograft(ui, repo, *revs, **opts):
     revs = list(revs)
     revs.extend(opts['rev'])
 
@@ -3837,7 +3844,6 b' def graft(ui, repo, *revs, **opts):'
         if not revs:
             return -1
 
-    wlock = repo.wlock()
     try:
         for pos, ctx in enumerate(repo.set("%ld", revs)):
             desc = '%d:%s "%s"' % (ctx.rev(), ctx,
@@ -3904,7 +3910,9 b' def graft(ui, repo, *revs, **opts):'
                     _('note: graft of %d:%s created no changes to commit\n') %
                     (ctx.rev(), ctx))
     finally:
-        wlock.release()
+        # TODO: get rid of this meaningless try/finally enclosing.
+        # this is kept only to reduce changes in a patch.
+        pass
 
     # remove state when we complete successfully
     if not opts.get('dry_run'):