Fix memory leaks in pg_rewind. Several PQclear() calls were missing.

Originally reported by Vladimir Borodin in the pg_rewind github project,
patch by Michael Paquier.

src/bin/pg_rewind/libpq_fetch.c

@@ -350,6 +350,8 @@ libpqGetFile(const char *filename, size_t *filesize)
 	memcpy(result, PQgetvalue(res, 0, 0), len);
 	result[len] = '\0';
 
+	PQclear(res);
+
 	pg_log(PG_DEBUG, "fetched file \"%s\", length %d\n", filename, len);
 
 	if (filesize)
@@ -410,6 +412,7 @@ libpq_executeFileMap(filemap_t *map)
 	if (PQresultStatus(res) != PGRES_COMMAND_OK)
 		pg_fatal("could not create temporary table: %s",
 				 PQresultErrorMessage(res));
+	PQclear(res);
 
 	sql = "COPY fetchchunks FROM STDIN";
 	res = PQexec(conn, sql);
@@ -417,6 +420,7 @@ libpq_executeFileMap(filemap_t *map)
 	if (PQresultStatus(res) != PGRES_COPY_IN)
 		pg_fatal("could not send file list: %s",
 				 PQresultErrorMessage(res));
+	PQclear(res);
 
 	for (i = 0; i < map->narray; i++)
 	{
@@ -464,6 +468,7 @@ libpq_executeFileMap(filemap_t *map)
 		if (PQresultStatus(res) != PGRES_COMMAND_OK)
 			pg_fatal("unexpected result while sending file list: %s",
 					 PQresultErrorMessage(res));
+		PQclear(res);
 	}
 
 	/*