Feature #4977: Add DownloadState information to Manifest, add saveToFile API
Feature #4977: Secure Downloader shared_ptr usage
Feature #4977: Support resume download in Downloader
Feature #4977: Support resume download with temporary Manifest file for AssetsManager
Feature #4977: Removed unused lines
Feature #4977: Removed unused lines
Merge pull request #53 from pandamicro/lua-vm-3.1.1

Feature #4977: Support resume download for AssetsManager