add rebuild the status of filefield in the mongo.

fix the problem about copying dir when lacking that dir.

app/models/filefield.rb

@@ -74,6 +74,9 @@ class Filefield
 		FileUtils.cd('..')
 		@back_foler = file_name.dup #very important,don't just use '=',it will change original value when it change
 		@back_foler[-1] = "_back/."
+		if !Dir.exist?(file_name)
+			FileUtils.mkdir_p file_name
+		end
 		FileUtils.cp_r(@back_foler, file_name)
 	end
   end
@@ -82,6 +85,9 @@ class Filefield
 	if (file_name.include? "/") == false
 		FileUtils.cp(file_name , dest_file_path)
 	else
+		if !Dir.exist?(dest_file_path)
+			FileUtils.mkdir_p dest_file_path
+		end
 		FileUtils.cp_r(file_name , dest_file_path+'..')
 	end
   end