fix up some pre-Python2.6 compatibility issues in the *dbm interface

Author: Richard Jones

roundup/backends/sessions_dbm.py

@@ -97,7 +97,7 @@ def set(self, infoid, **newvalues):
     def list(self):
         db = self.opendb('r')
         try:
-            return list(db)
+            return list(db.keys())
         finally:
             db.close()