#18 Header ssl detection support

[Kevin]

We are using a load balancer to answer ssl and non-ssl
requests. The load balancer handles the certificate
and forwards the ssl request in clear text to the
application server to be answered on the same non-ssl
port. We have the ability to inject headers on ssl
requests from the load balancer for use by our
application to detect ssl.

We would like to see some way to configure sslext in
struts to handle header keys existing or not existing
to detect ssl along with the current port settings.

Another feature to build upon the header key would be
the use of header values for http and https ssl detection.