Captive Portal modification to allow SIP2 authentication

This contribution will allow public libraries to authenticate patrons against their ILS software.
It can be configured to prevent patrons with excessive fines from authenticating, and should work with
any SIP2 compliant ISL. (most of them)
Tested and known to work with Evergreen and Sirsi. 
http://en.wikipedia.org/wiki/Standard_Interchange_Protocol