Ensure that config file is closed immediately

flask/config.py

@@ -125,7 +125,8 @@ class Config(dict):
         d = imp.new_module('config')
         d.__file__ = filename
         try:
-            exec(compile(open(filename).read(), filename, 'exec'), d.__dict__)
+            with open(filename) as config_file:
+                exec(compile(config_file.read(), filename, 'exec'), d.__dict__)
         except IOError as e:
             if silent and e.errno in (errno.ENOENT, errno.EISDIR):
                 return False