Fix some of the warnings that come up in the migration tool: urldecode url...

Fix some of the warnings that come up in the migration tool: urldecode url before looking the file up on frontier, suppress warnings (duplicate dir was the problem) coming from mkdir, make sure there's a '/' between ftp base and path before getting modified time

git-svn-id: file:///tmp/wdn_thm_drupal/branches/drupal-7.x@157 20a16fea-79d4-4915-8869-1ea9d5ebf173