fix cached file type, and cache whether the filesystem is read only

MTFS/OpenOS/usr/bin/importfs.lua

@@ -44,7 +44,7 @@ if px.dirstat then -- use single call for file info
   end
   local ci = statcache["/"..fs.canonical(p)]
   if ci then
-   return ci[3]
+   return ci[n]
   end
  end
  function px.isDirectory(path)
@@ -57,4 +57,8 @@ if px.dirstat then -- use single call for file info
   return gce(path, 4) or olm(path)
  end
 end
+local iro = px.isReadOnly()
+function px.isReadOnly()
+ return iro
+end
 fs.mount(px, lpath)