do not allow ndb files to go stale.  make sure they are reopened

Reference: /n/atom/patch/applied2013/ndbdbreopen
Date: Thu Jun 20 00:28:20 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/ndb/dblookup.c	Thu Jun 20 00:27:33 2013
+++ /sys/src/cmd/ndb/dblookup.c	Thu Jun 20 00:27:33 2013
@@ -63,13 +63,17 @@
 }
 
 int
-opendatabase(void)
+opendatabase0(int reopen)
 {
 	char netdbnm[256];
 	Ndb *xdb, *netdb;
-
-	if (db)
-		return 0;
+	
+	if(db){
+		if(!reopen)
+			return 0;
+		db = ndbreopendb(db);
+		return db? 0: -1;
+	}
 
 	xdb = ndbopen(dbfile);		/* /lib/ndb */
 
@@ -82,6 +86,12 @@
 	return db? 0: -1;
 }
 
+int
+opendatabase(void)
+{
+	return opendatabase0(0);
+}
+
 /*
  *  lookup an RR in the network database, look for matches
  *  against both the domain name and the wildcarded domain name.
@@ -706,7 +716,7 @@
 
 	lock(&dblock);
 
-	if(opendatabase() < 0){
+	if(opendatabase0(1) < 0){
 		unlock(&dblock);
 		return;
 	}
@@ -736,7 +746,7 @@
 		freearea(&owned);
 		freearea(&delegated);
 
-		/* reopen all the files (to get oldest for time stamp) */
+		/* reopen all the files (to get oldest for time stamp) necessary with opendatabase0? */
 		for(ndb = db; ndb; ndb = ndb->next)
 			ndbreopen(ndb);