shelve: widen wlock scope of unshelve for consistency while processing

Before this patch, "hg unshelve" of shelve extension executes below
before acquisition of wlock:

  - cmdutil.checkunfinished()
  - examine existence of (specified) shelve file

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

This patch widens wlock scope of "hg unshelve" of shelve extension for
consistency while processing.

hgext/shelve.py

@@ -616,6 +616,13 b' def unshelve(ui, repo, *shelved, **opts)'
        than ``maxbackups`` backups are kept, if same timestamp
        prevents from deciding exact order of them, for safety.
     """
+    wlock = repo.wlock()
+    try:
+        return _dounshelve(ui, repo, *shelved, **opts)
+    finally:
+        lockmod.release(wlock)
+
+def _dounshelve(ui, repo, *shelved, **opts):
     abortf = opts['abort']
     continuef = opts['continue']
     if not abortf and not continuef:
@@ -656,11 +663,10 b' def unshelve(ui, repo, *shelved, **opts)'
         raise error.Abort(_("shelved change '%s' not found") % basename)
 
     oldquiet = ui.quiet
-    wlock = lock = tr = None
+    lock = tr = None
     forcemerge = ui.backupconfig('ui', 'forcemerge')
     try:
         ui.setconfig('ui', 'forcemerge', opts.get('tool', ''), 'unshelve')
-        wlock = repo.wlock()
         lock = repo.lock()
 
         tr = repo.transaction('unshelve', report=lambda x: None)
@@ -755,7 +761,7 b' def unshelve(ui, repo, *shelved, **opts)'
         ui.quiet = oldquiet
         if tr:
             tr.release()
-        lockmod.release(lock, wlock)
+        lockmod.release(lock)
         ui.restoreconfig(forcemerge)
 
 @command('shelve',