Change delimiter used for display of NextXID

NextXID has been rendered in the form of a pg_lsn even though it
really is not. This can cause confusion, so change the format from
%u/%u to %u:%u, per discussion on hackers.

Complaint by me, patch by me and Bruce, reviewed by Michael Paquier
and Alvaro. Applied to HEAD only.

Author: Joe Conway, Bruce Momjian
Reviewed-by: Michael Paquier, Alvaro Herrera
Backpatch-through: master

src/backend/access/rmgrdesc/xlogdesc.c

@@ -43,7 +43,7 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
 		CheckPoint *checkpoint = (CheckPoint *) rec;
 
 		appendStringInfo(buf, "redo %X/%X; "
-						 "tli %u; prev tli %u; fpw %s; xid %u/%u; oid %u; multi %u; offset %u; "
+						 "tli %u; prev tli %u; fpw %s; xid %u:%u; oid %u; multi %u; offset %u; "
 						 "oldest xid %u in DB %u; oldest multi %u in DB %u; "
 						 "oldest/newest commit timestamp xid: %u/%u; "
 						 "oldest running xid %u; %s",

src/backend/access/transam/xlog.c

@@ -6283,7 +6283,7 @@ StartupXLOG(void)
 				  (uint32) (checkPoint.redo >> 32), (uint32) checkPoint.redo,
 					wasShutdown ? "TRUE" : "FALSE")));
 	ereport(DEBUG1,
-			(errmsg_internal("next transaction ID: %u/%u; next OID: %u",
+			(errmsg_internal("next transaction ID: %u:%u; next OID: %u",
 					checkPoint.nextXidEpoch, checkPoint.nextXid,
 					checkPoint.nextOid)));
 	ereport(DEBUG1,