Avoid macro expansion if open() is a macro.

diff -up nss_db-2.2/db-compat.c nss_db-2.2/db-compat.c
--- nss_db-2.2/db-compat.c	2007-08-14 10:05:07.000000000 -0400
+++ nss_db-2.2/db-compat.c	2007-08-14 10:05:09.000000000 -0400
@@ -39,7 +39,7 @@ db_open (const char *file, DBTYPE type, 
   if (err)
     return err;
 
-  err = db->open (db, NULL, file, NULL, type, flags, mode);
+  err = (db->open) (db, NULL, file, NULL, type, flags, mode);
   if (err)
     {
       db->close (db, 0);