Fix bug in pg_basebackup -F plain -R.

Commit caba97a9 changed pg_basebackup -F plain -R so that
it overwrote postgresql.auto.conf in the backup, with new connection
setting. This could cause the existing postgresql.auto.conf settings
in the server to get lost unexpectedly. This is a bug.

This commit fixes the bug by making pg_basebackup -F plain -R
append the connection setting into postgresql.auto.conf in the backup.

Author: Fujii Masao
Reviewed-by: Sergei Kornilov
Discussion: https://postgr.es/m/250dcf2a-94e7-c05e-824a-73cfb38a48a4@oss.nttdata.com

src/fe_utils/recovery_gen.c

@@ -128,7 +128,7 @@ WriteRecoveryConfig(PGconn *pgconn, char *target_dir, PQExpBuffer contents)
 	snprintf(filename, MAXPGPATH, "%s/%s", target_dir,
 			 use_recovery_conf ? "recovery.conf" : "postgresql.auto.conf");
 
-	cf = fopen(filename, use_recovery_conf ? "a" : "w");
+	cf = fopen(filename, use_recovery_conf ? "w" : "a");
 	if (cf == NULL)
 	{
 		pg_log_error("could not open file \"%s\": %m", filename);