SysLoggerMain: fix timestamp delay code

Log rotations were happening well after the timestamp on the log file
(e.g. a per-minute rotation might actually take place thirty seconds
after it was supposed to).

After the 9.2 merge, we were incorrectly shadowing the `now` variable,
so the rotation delay only got bigger and bigger. Periodic logging (such
as from FTS) caused us to break out of the wait by luck, but otherwise
the syslogger would take longer and longer to wake up to perform a
rotation.
Co-authored-by: NJamie McAtamney <jmcatamney@pivotal.io>

src/backend/postmaster/syslogger.c

@@ -497,8 +497,7 @@ SysLoggerMain(int argc, char *argv[])
 		if (Log_RotationAge > 0 && !rotation_disabled)
 		{
 			/* Do a logfile rotation if it's time */
-			pg_time_t	now = (pg_time_t) time(NULL);
-
+			now = (pg_time_t) time(NULL);
 			if (now >= next_rotation_time)
 			{
 				rotation_requested = time_based_rotation = true;