Forward a StoreEntry holding the bumped secure connection establishment

Forward a StoreEntry holding the bumped secure connection establishment
error page from the server-side code (which generates the error) to the
client-side code (which delays the error until the first encrypted
request comes). This allows Squid to display the error page to the user
(using secure connection) when bumping intercepted SSL connections. The
code still needs more polishing, including generating errors with host
names and not IP addresses (when possible).

The peeked server certificate is now stored in
ConnStateData::bumpErrorEntry. This allows us to mimic the certificate
of dropped server connections.

Load signing certificate and key when initializing a tproxy-enabled
https_port.

Fixed debugging when opening a peeking connection.