Allow the X-Forwarded-* to be set to single host

Some app server (Django) do not support lists for X-Forwarded-Server or
X-Forwarded-Host. This change allows those headers to be proxied on
their own.

On Django specifically; they have stated that they will not fix.
https://code.djangoproject.com/ticket/9064
Ignore .bundle directory
Merge pull request #18 from alphagov/set-forwarded-host-2

Allow the X-Forwarded-* to be set to single host