configitems: register the 'web.allowbz2' config

mercurial/configitems.py

@@ -712,6 +712,9 b" coreconfigitem('ui', 'verbose',"
 coreconfigitem('verify', 'skipflags',
     default=None,
 )
+coreconfigitem('web', 'allowbz2',
+    default=None,
+)
 coreconfigitem('web', 'accesslog',
     default='-',
 )