module Rack::Utils

def set_cookie_header!(headers, key, value)

to an +Array+ if not already, and appended to.
If the headers already contains a +set-cookie+ key, it will be converted

+value+ using set_cookie_header.
Append a cookie in the specified headers with the given cookie +key+ and

set_cookie_header!(headers, key, value) -> header value
:call-seq: 
def set_cookie_header!(headers, key, value)
  if header = headers[SET_COOKIE]
    if header.is_a?(Array)
      header << set_cookie_header(key, value)
    else
      headers[SET_COOKIE] = [header, set_cookie_header(key, value)]
    end
  else
    headers[SET_COOKIE] = set_cookie_header(key, value)
  end
end