remove memory leak from creating persistent strings

src/statement.cc

@@ -100,7 +100,7 @@ Handle<Value> Statement::New(const Arguments& args) {
     Database* db = ObjectWrap::Unwrap<Database>(args[0]->ToObject());
     Local<String> sql = Local<String>::Cast(args[1]);
 
-    args.This()->Set(String::NewSymbol("sql"), Persistent<String>::New(sql), ReadOnly);
+    args.This()->Set(String::NewSymbol("sql"), sql, ReadOnly);
 
     Statement* stmt = new Statement(db);
     stmt->Wrap(args.This());

test/prepare.test.js

@@ -67,7 +67,10 @@ exports['test inserting and retrieving rows'] = function(beforeExit) {
         function(err, rows) {
             if (err) throw err;
             inserted += rows.length;
-            var stmt = db.prepare("SELECT txt, num, flt, blb FROM foo ORDER BY num");
+            var stmt = db.prepare("SELECT txt, num, flt, blb FROM foo ORDER BY num", function(err) {
+                if (err) throw err;
+                assert.equal(stmt.sql, 'SELECT txt, num, flt, blb FROM foo ORDER BY num');
+            });
 
             var group = this.group();
             for (var i = 0; i < count + 5; i++) {