Support aka.foo.com == www.foo.com aka hostnames

We use a different aka hostname based on whether or not the original hostname
began with 'www.'. I know this because we have tests in redirector which try to
use http://aka.homeoffice.gov.uk which pass against redirector but fail against
bouncer.
Merge pull request #27 from alphagov/support_both_aka_hostname_behaviours

Support aka.foo.com == www.foo.com aka hostnames