Advanced session hijacking mitigation

utilizing ssl_session_id (when mod_ssl is enabled) and ip/user-agent
when using raw http connections an additional check is done to ensure
that cooked are not copied between systems thus preventing session
hijacking

If a user with a valid CAS session attempts to copy another user's
cookie the existing CAS session will simply reestablish and the stolen
cookie will be invalidated.
While this could potentially create a denial of service; the risk is
limited to non-https connections.

In addition the isSSL function now utilizes the mod_ssl optional function ssl_is_https 
The mod_ssl_is_https static is an apache optional (APR_OPTIONAL_FN_TYPE) and would be NULL if not registered by an alternate module. The goal was to used the apache style method when available and then string comparison if the former is unavailable.