update heroku.py to the new pydal

gluon/contrib/heroku.py

@@ -7,15 +7,13 @@ db = get_db()
 """
 import os
 from gluon import *
-from pydal.adapters import ADAPTERS, PostgreSQLAdapter
+from pydal.adapters import adapters, PostgrePsyco
 from pydal.helpers.classes import UseDatabaseStoredFile
 
-class HerokuPostgresAdapter(UseDatabaseStoredFile,PostgreSQLAdapter):
-    drivers = ('psycopg2',)
+@adapters.register_for('postgres')
+class HerokuPostgresAdapter(DatabaseStoredFile, PostgrePsyco):
     uploads_in_blob = True
 
-ADAPTERS['postgres'] = HerokuPostgresAdapter
-
 def get_db(name = None, pool_size=10):
     if not name:
         names = [n for n in os.environ.keys()