Alternate origin server selection

[Opendium]

When the proxy is making a direct connection to the origin server, it will now connect to the host contained in the alt-host note, or X-Alt-Host ICAP response header, if such a note / header exists. This allows an external ACL or ICAP server to redirect the request to a different host.

This is useful where services have a specific "virtual IP" that clients can connect to to receive a modified service. e.g. this can be used to force the "Safe Search" feature on for certain search engines.

[squid-prbot]

Can one of the admins verify this patch?

[rousskov]

FWIW, I recommend avoiding PR code changes until everybody involved is on the same page with regard to what should be changed.