configitems: register the 'histedit.defaultrev' config

hgext/histedit.py

@@ -188,6 +188,7 b' from mercurial.i18n import _'
 from mercurial import (
     bundle2,
     cmdutil,
+    configitems,
     context,
     copies,
     destutil,
@@ -212,6 +213,12 b' release = lock.release'
 cmdtable = {}
 command = registrar.command(cmdtable)
 
+configtable = {}
+configitem = registrar.configitem(configtable)
+configitem('histedit', 'defaultrev',
+    default=configitems.dynamicdefault,
+)
+
 # Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
 # extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
 # be specifying the version(s) of Mercurial they are tested with, or