Fix/to xml yaml type

Reposman.rb fails beginning with rails 2.3.15 as long as the plugin leads to the Repository#to_xml method outputting a <checkout-settings type="yaml"> node. 

The logfile output is:
Unable to connect to http://dev.finn.de/sys/: Disallowed type attribute: "yaml"

This is due to the fact that Reposman.rb defines an ActiveResource reading from SysController#projects. As the projects' xml representation includes a yaml typed node, the deserialization fails. 

The code was only tested with OpenProject. It should however work for Redmine and ChiliProject as well.