Add line-by-line support to old dev_appserver

Summary: I haven't tested this in 1.8 but it uses the same code as webapp/config_jinja.py does to allow _ctypes and gestalt so I assume it works.

Reviewers: jlfwong

Reviewed By: jlfwong

Differential Revision: http://phabricator.khanacademy.org/D5236