registrar: host "dynamicdefault" constant by configitem object

This is the common pattern seen in the other registrar classes.

hgext/bugzilla.py

@@ -301,7 +301,6 b' from mercurial.i18n import _'
 from mercurial.node import short
 from mercurial import (
     cmdutil,
-    configitems,
     error,
     mail,
     registrar,
@@ -354,7 +353,7 b" configitem('bugzilla', 'host',"
     default='localhost',
 )
 configitem('bugzilla', 'notify',
-    default=configitems.dynamicdefault,
+    default=configitem.dynamicdefault,
 )
 configitem('bugzilla', 'password',
     default=None,

hgext/histedit.py

@@ -190,7 +190,6 b' from mercurial.i18n import _'
 from mercurial import (
     bundle2,
     cmdutil,
-    configitems,
     context,
     copies,
     destutil,
@@ -221,7 +220,7 b" configitem('experimental', 'histedit.aut"
     default=False,
 )
 configitem('histedit', 'defaultrev',
-    default=configitems.dynamicdefault,
+    default=configitem.dynamicdefault,
 )
 configitem('histedit', 'dropmissing',
     default=False,

hgext/largefiles/__init__.py

@@ -107,7 +107,6 b' command.'
 from __future__ import absolute_import
 
 from mercurial import (
-    configitems,
     hg,
     localrepo,
     registrar,
@@ -131,7 +130,7 b' configtable = {}'
 configitem = registrar.configitem(configtable)
 
 configitem('largefiles', 'minsize',
-    default=configitems.dynamicdefault,
+    default=configitem.dynamicdefault,
 )
 configitem('largefiles', 'patterns',
     default=list,

mercurial/configitems.py

@@ -106,7 +106,10 b' dynamicdefault = object()'
 # Registering actual config items
 
 def getitemregister(configtable):
-    return functools.partial(_register, configtable)
+    f = functools.partial(_register, configtable)
+    # export pseudo enum as configitem.*
+    f.dynamicdefault = dynamicdefault
+    return f
 
 coreconfigitem = getitemregister(coreitems)