Improve phrasing of warning message for NOTIFY queue getting too full.

Per gripe from Peter.

src/backend/commands/async.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.155 2010/02/26 02:00:37 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.156 2010/04/05 00:42:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1421,12 +1421,12 @@ asyncQueueFillWarning(void)
 		}
 
 		ereport(WARNING,
-				(errmsg("pg_notify queue is %.0f%% full", fillDegree * 100),
+				(errmsg("NOTIFY queue is %.0f%% full", fillDegree * 100),
 				 (minPid != InvalidPid ?
-				  errdetail("PID %d is among the slowest backends.", minPid)
+				  errdetail("The server process with PID %d is among those with the oldest transactions.", minPid)
 				  : 0),
 				 (minPid != InvalidPid ?
-				  errhint("Cleanup can only proceed if this backend ends its current transaction.")
+				  errhint("The NOTIFY queue cannot be emptied until that process ends its current transaction.")
 				  : 0)));
 
 		asyncQueueControl->lastQueueFillWarn = t;