KFileWizard: skip the entries of a directory whose copy fails
FtpTransferThread: try to close FTP connection on abort
KFileWizard: refresh FTP dir manually again

Refreshing on close() has too much overhead.
Reenable ftp connection cacheEntry

commit 2db63992a516654e990b1ef09e701d27409b1b2d solved the
problems releated to connection cache