Allow importing old databases.

Currently:
- Minetest (`ipban.txt')
- xban v1 (`players.iplist')

dbimport.lua

@@ -0,0 +1,37 @@
+
+xban.importers = { }
+
+dofile(xban.MP.."/importers/minetest.lua")
+dofile(xban.MP.."/importers/v1.lua")
+
+minetest.register_chatcommand("xban_dbi", {
+	description = "Import old databases",
+	params = "<importer>",
+	privs = { server=true },
+	func = function(name, params)
+		if params == "--list" then
+			local names = { }
+			for name in pairs(xban.importers) do
+				table.insert(names, name)
+			end
+			minetest.chat_send_player(name,
+			  ("[xban] Known importers: %s"):format(
+			  table.concat(names, ", ")))
+			return
+		elseif not xban.importers[params] then
+			minetest.chat_send_player(name,
+			  ("[xban] Unknown importer `%s'"):format(params))
+			minetest.chat_send_player(name, "[xban] Try `--list'")
+			return
+		end
+		local f = xban.importers[params]
+		local ok, err = f()
+		if ok then
+			minetest.chat_send_player(name,
+			  "[xban] Import successfull")
+		else
+			minetest.chat_send_player(name,
+			  ("[xban] Import failed: %s"):format(err))
+		end
+	end,
+})