Support a database-local fsync setting. Needs berkeley db patch.

--- ./lib/backend/db3.c.orig	2017-01-19 10:31:06.874215725 +0000
+++ ./lib/backend/db3.c	2017-01-19 10:32:51.825873926 +0000
@@ -73,8 +73,10 @@ static const struct poptOption rdbOption
  { "mp_size",	0,POPT_ARG_INT,		&staticcfg.db_cachesize, 0,
 	NULL, NULL },
 
+#if 0
  { "nofsync",	0,POPT_ARG_NONE,	&staticcfg.db_no_fsync, 0,
 	NULL, NULL },
+#endif
 
  /* Per-dbi options */
  { "nommap",	0,POPT_BIT_SET,		&staticdbicfg.dbi_oflags, DB_NOMMAP,
@@ -84,6 +86,8 @@ static const struct poptOption rdbOption
 	NULL, NULL },
  { "lockdbfd",	0,POPT_ARG_NONE,	&staticdbicfg.dbi_lockdbfd, 0,
 	NULL, NULL },
+ { "nofsync",	0,POPT_BIT_SET,		&staticdbicfg.dbi_oflags, DB_NOFSYNC,
+	NULL, NULL },
 
     POPT_TABLEEND
 };