Complain about status code before content type.
Complain about status code before content type.

GitHub currently returns 500 errors as HTML. When we encountered this, the
error message referred to the content type rather than the status code. Now we
check the status code first, so errors are more informative.

Signed-off-by: Felipe Coury <413bed34e59799564bf802e742f91eee94580e4a@gmail.com>
fcoury/octopi,fcoury/octopi,fcoury/octopi