Add support to Bro for connecting with peers over IPv6.

- Communication::listen_ipv6 needs to be redef'd to true in order
  for IPv6 listening sockets to be opened.

- Added Communication::listen_retry option as an interval at which
  to retry binding to socket addresses that were already in use.

- Added some explicit baselines to check in the istate.events
  and istate.events-ssl tests -- the SSL test was incorrectly
  passing because it compared two empty files.  (The files being
  empty because "http/base" was given as an argument to Bro which
  it couldn't handle because that script doesn't exist anymore).

scripts/base/utils/addrs.bro

@@ -98,3 +98,18 @@ function find_ip_addresses(input: string): string_array
 		}
 	return output;
 	}
+
+## Returns the string representation of an IP address suitable for inclusion
+## in a URI.  For IPv4, this does no special formatting, but for IPv6, the
+## address is included in square brackets.
+##
+## a: the address to make suitable for URI inclusion.
+##
+## Returns: the string representation of *a* suitable for URI inclusion.
+function addr_to_uri(a: addr): string
+	{
+	if ( is_v4_addr(a) )
+		return fmt("%s", a);
+	else
+		return fmt("[%s]", a);
+	}