make unionfs a more ... optional dependency of netutil

lib/netutil.lua

@@ -1,7 +1,6 @@
 local computer = require "computer"
 local minitel = require "minitel"
 local event = require "event"
-local ufs = require "unionfs"
 local rpc = require "rpc"
 local netutil = {}
 
@@ -16,7 +15,7 @@ end
 
 function netutil.exportfs(path) -- string -- boolean -- Export the directory *path* over RPC.
  local path = "/"..table.concat(fs.segments(path),"/")
- local px = ufs.create(path)
+ local px = require("unionfs").create(path)
  for k,v in pairs(px) do
   rpc.register(path.."_"..k,v)
   print(path.."_"..k)