fix download path and commodity show  images url

in IOS, app read or write files  in own private space.  like:
read a file  /test/1.txt,
indeed the real path is  xxx/xxx/xx/document/test/1.txt
in phonegap most file api  automatic mapping path to private
space ,but some api not. the download api is!
how to fix download: get  private space full path and add to download
path front !
commodity show images url  has sam problem.  fix like download problem