In get_placeholder_conf check value against None to allow '0' as a valid configuration value
Remove python 2.5 from travis:
See http://about.travis-ci.org/blog/2013-11-18-upcoming-build-environment-updates/
Merge pull request #2369 from yakky/feature/remove_py25

Remove python 2.5 from travis
Merge pull request #2367 from yakky/feature/check_noneness_23

Backport of #2365 to 2.3