configitems: register the 'worker.backgroundcloseminfilecount' config

mercurial/configitems.py

@@ -158,3 +158,6 b" coreconfigitem('ui', 'quiet',"
 coreconfigitem('worker', 'backgroundclosemaxqueue',
     default=384,
 )
+coreconfigitem('worker', 'backgroundcloseminfilecount',
+    default=2048,
+)

mercurial/vfs.py

@@ -541,8 +541,7 b' class backgroundfilecloser(object):'
         # There is overhead to starting and stopping the background threads.
         # Don't do background processing unless the file count is large enough
         # to justify it.
-        minfilecount = ui.configint('worker', 'backgroundcloseminfilecount',
-                                    2048)
+        minfilecount = ui.configint('worker', 'backgroundcloseminfilecount')
         # FUTURE dynamically start background threads after minfilecount closes.
         # (We don't currently have any callers that don't know their file count)
         if expectedcount > 0 and expectedcount < minfilecount: