Bug 5189: Preserve configured order of intermediate CA certificate chain (#956)

Bug 5189: Preserve configured order of intermediate CA certificate chain (#956)

    https_port ... tls-cert=signing,itsIssuer,itsIssuerIssuer.pem

The order was reversed in commit cf48712, probably by accident. Wrong
order violates TLS protocol and breaks TLS clients that are incapable of
reordering received intermediate CAs. Squid deployments that use
wrong-order bundles (to compensate for this bug) should reorder their
bundles when deploying this fix (or wait for Squid to order certificates
correctly, regardless of the bundle order -- a work in progress).

This is a Measurement Factory project.