use faster command to correct imap spool permissions

After copy of the imap spool, use find/xargs to correct permissions. This is a lot faster than "find -exec". In case someone still has find without -print0 or xargs without -0 keep the old commands as fallback.

While at it, correct the find commands to display "\;" after -exec.
Merge pull request #13 from jh23453/patch-2

use faster command to correct imap spool permissions