Proof of concept: support delegating deferredOpen

Author: vweevers

lib/levelup.js

@@ -54,10 +54,10 @@ function LevelUP (db, options, callback) {
 
   this.options = getOptions(options)
   this._db = db
-  this.db = new DeferredLevelDOWN(db)
+  this.db = db.supports && db.supports.deferredOpen ? db : new DeferredLevelDOWN(db)
   this.open(callback)
 
-  // Create manifest based on deferred-leveldown's
+  // Create manifest based on db or deferred-leveldown's
   this.supports = supports(this.db.supports, {
     status: false,
     deferredOpen: true,