configitems: register the 'devel.cache-vfs' config

mercurial/configitems.py

@@ -116,6 +116,9 b" coreconfigitem('devel', 'all-warnings',"
 coreconfigitem('devel', 'bundle2.debug',
     default=False,
 )
+coreconfigitem('devel', 'cache-vfs',
+    default=None,
+)
 coreconfigitem('devel', 'check-locks',
     default=False,
 )