for the JSON database 'engine', don't write database at close. This was...

for the JSON database 'engine', don't write database at close.  This was causing browserid to stomp changes made be dbwriter during tests where server restart occurs (like bcrypt password update test) - *really* closes issue #557

lib/db/json.js

@@ -106,12 +106,13 @@ exports.open = function(cfg, cb) {
 };
 
 exports.closeAndRemove = function(cb) {
-  flush();
   fs.unlink(dbPath, function(err) { cb(err === null ? undefined : err); });
 };
 
 exports.close = function(cb) {
-  flush();
+  // don't flush database here to disk, the database is flushed synchronously when
+  // written - If we were to flush here we could overwrite changes made by
+  // another process - see issue #557
   setTimeout(function() { cb(undefined) }, 0);
 };