PATCH: numeric timestamp in log_line_prefix

Hi,

from time to time I need to correlate PostgreSQL logs to other logs,
containing numeric timestamps - a prime example of that is pgbench. With
%t and %m that's not quite trivial, because of timezones etc.

I propose adding two new log_line_prefix escape sequences - %T and %M,
doing the same thing as %t and %m, but formatting the value as a number.

Patch attached, I'll add it to CF 2015-06.

regards

--
Tomas Vondra                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services