fix issue for ConfigParser.NoOptionError: No option 'urlfilter' in section: 'pac'

http://code.google.com/p/goagent/issues/detail?id=10319
https://github.com/goagent/goagent/commit/06a8fb55329a2ee229694037c060e9
cdf10d970c
Merge pull request #197 from lwr/master

fix issue for ConfigParser.NoOptionError: No option 'urlfilter' in section: 'pac'