In TProofMgr, add support for the following functionality:
       - sandbox file listing and browsing
       - sandbox file removal
       - file upload, download
   See http://root.cern.ch/drupal/content/accessing-sandbox for details.


git-svn-id: http://root.cern.ch/svn/root/trunk@29579 27541ba8-7e3a-0410-8455-c3a389f83636