Write correct file name in "START WAL LOCATION" backup_label's field

ThisTimeLineID is always 0 in a normal backend during recovery.
We get latest redo apply position timeline and we update it globally
to make do_pg_start_backup using the correct value when generate the
backup label text

.gitignore

@@ -1,2 +1,3 @@
 *.so
 *.o
+.deps/

pgespresso.c

@@ -53,6 +53,7 @@ pgespresso_start_backup(PG_FUNCTION_ARGS)
 	char	   *backupidstr;
 	XLogRecPtr	startpoint;
 	char       *labelfile;
+	TimeLineID  replayTLI;
 
 	backupidstr = text_to_cstring(backupid);
 
@@ -61,6 +62,18 @@ pgespresso_start_backup(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 		   errmsg("must be superuser or replication role to run a backup")));
 
+	/*
+	 * ThisTimeLineID is always 0 in a normal backend during recovery.
+	 * We get latest redo apply position timeline and we update it globally
+	 * to make do_pg_start_backup use the correct value when generating
+	 * backup label text
+	 */
+	if (RecoveryInProgress()) {
+	  GetXLogReplayRecPtr(&replayTLI);
+	  ThisTimeLineID = replayTLI;
+	  elog(DEBUG1, "updated ThisTimeLineID = %u", ThisTimeLineID);
+	}
+
 	startpoint = do_pg_start_backup(backupidstr, fast, NULL, &labelfile);
 
 	PG_RETURN_TEXT_P(cstring_to_text(labelfile));