http://doughellmann.com/2012/11/12/the-performance-impact-of-using-dict-instead-of-in-cpython-2-7-2.html

Because not all sources might offer one

Resolved conflicts:
	django/website/local_settings.py.jenkins

...so that bootstrap building does not fail on syntax error anymore.

This eliminates warnings about the default value for this attribute
changing.

The default branch on staging was set to 'master'. This led to the
staging server not working because the wrong branch had been deployed.