Added clientside_mark ACL for checking CONNMARK (#111)

Added clientside_mark ACL for checking CONNMARK (#111)

Matches CONNMARK of accepted connections. Takes into account
clientside_mark and qos_flows mark changes (because Squid-set marks are
cached by Squid in conn->nfmark). Ignores 3rd-party marks set after
Squid has accepted the connection from a client (because Squid never
re-queries the connection to update/sync conn->nfmark).

Also added a debugs()-friendly API to print hex values.