Abort OpenId responses with headers over 8kb
    
    They will not be able to be returned through Apache, and if we don't
    error this way, Apache will log obscure things.
    
    This will happen if a user for example has 3 16KB SSH keys (live
    example seen), and they are all requested.
    OpenID 2.0 wants to encode the entire response in an HTTP Location
    header, but when Apache sees this in the headers, it thinks we
    made a mistake, and aborts the response.
    
    Ticket: #238
    Merges: #168
    Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>
    Reviewed-by: Howard Johnson <merlin@merlinthp.org>