Main optimization consists in reducing disk writes, by not using 'copytree'
anymore. Only modified/new files are copied from the temporary folder.

Also drop 'copyTree' and 'cacheWalk' because they are unused and 'dircache' is
deprecated.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@40326 20353a03-c40f-0410-a6d1-a30d3c3de9de