configitems: register the 'rebase.singletransaction' config

hgext/rebase.py

@@ -83,6 +83,9 b" configitem('commands', 'rebase.requirede"
 configitem('experimental', 'rebaseskipobsolete',
     default=True,
 )
+configitem('rebase', 'singletransaction',
+    default=False,
+)
 
 def _nothingtorebase():
     return 1