log_line_info

I think this is now ready for application, unless someone objects.

Since the last patch I posted, I have done the following:

. changed the escapes to lower case, as Peter prefers. This is also in
line with what Apache does, which is the nearest equivalent I can think of.
. added 2 new escapes: %r = remote host and port and %x says "postmaster
and friends stop here". Postmaster and friends will also ignore any
escapes they see that don't make sense (specifically %u %d %i %r %s and
%c). However, they no longer ignore the whole facility. This means we
can use it for logging (for example) timestamps and pids in all cases.
. added docco
. changed source port reporting from host:port to host(port) to avoid
IP6 address ambiguity.

If someone wants to monkey with the name of the facility, it shouldn't
be hard. I don't like plain "log_line", though. "log_line_prefix" or
"log_line_tag" both seem to me better alternatives.

After this is applied (fingers crossed) and everyone is happy, I will
submit a patch to remove log_timestamp, log_pid and (if we are agreed on
it) log_source_port.

cheers

andrew