upgrade: use actual filelog to convert filelog

Extensions can add extra logic related to the config, so we must use the actual
class. The path used needs minimal transformation for this to work.

mercurial/upgrade.py

@@ -14,6 +14,7 b' from .i18n import _'
 from . import (
     changelog,
     error,
+    filelog,
     hg,
     localrepo,
     manifest,
@@ -413,9 +414,8 b' def _revlogfrompath(repo, path):'
         mandir = path[:-len('00manifest.i')]
         return manifest.manifestrevlog(repo.svfs, dir=mandir)
     else:
-        # Filelogs don't do anything special with settings. So we can use a
-        # vanilla revlog.
-        return revlog.revlog(repo.svfs, path)
+        #reverse of "/".join(("data", path + ".i"))
+        return filelog.filelog(repo.svfs, path[5:-2])
 
 def _copyrevlogs(ui, srcrepo, dstrepo, tr, deltareuse, aggressivemergedeltas):
     """Copy revlogs between 2 repos."""