vac: additionally flush venti directory files when flushing directory metadata files

src/cmd/vac/file.c

Index: src/cmd/vac/file.c 
=================================================================== 
--- a/src/cmd/vac/file.c 
+++ b/src/cmd/vac/file.c 
@@ -983,6 +983,7 @@ 
 
	/* No block found, extend the file by one metablock. */ 
	vtfileflushbefore(ms, nb*(uvlong)ms->dsize); 
+	vtfileflushbefore(fp->source, VtEntrySize*(uvlong)dir->entry); 
	if((b = vtfileblock(ms, nb, VtORDWR)) == nil) 
	goto Err; 
	vtfilesetsize(ms, (nb+1)*ms->dsize);