modified titanftp_xcrc_traversal to allow RHOSTS

This pull request will allow for RHOSTS and THREADS as requested in redmine here:
http://dev.metasploit.com/redmine/issues/7719

Original Pull Request:  https://github.com/rapid7/metasploit-framework/pull/1377

The module has not been moved to the auxiliary/scanner/ftp directory since it is now a scanner module.