fast-export: Do parent rewriting to avoid dropping relevant commits

When specifying paths to export, parent rewriting must be turned on for
fast-export to output anything at all.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-fast-export.c

@@ -531,6 +531,7 @@ int cmd_fast_export(int argc, const char **argv, const char *prefix)
 	init_revisions(&revs, prefix);
 	revs.topo_order = 1;
 	revs.show_source = 1;
+	revs.rewrite_parents = 1;
 	argc = setup_revisions(argc, argv, &revs, NULL);
 	argc = parse_options(argc, argv, prefix, options, fast_export_usage, 0);
 	if (argc > 1)