IDP-1655 - Add root PGT support to CAS EncodingTicketService

[Paul B. Henson]

I updated the CAS EncodingTicketService to support encoding root proxy 
granting tickets to allow HA without requiring server-side storage, at 
least in the case where there is only one level of proxying involved. I 
submitted an issue with the patch:

https://issues.shibboleth.net/jira/browse/IDP-1655

I've done some testing and believe it functions correctly, although some 
of the specific implementation details might not be ideal. I would 
greatly appreciate any feedback or suggestions regarding it, thanks much…