* url-queue.el (url-queue-kill-job): Delete the process sentinel
before killing the process to avoid a race condition between the
two processes killing off the process buffer.
* url-queue.el (url-queue-callback-function): Remove the job from
the queue so that we don't kill the current buffer, which will
then make the callback function kill a random buffer.
* url-http.el (url-http-create-request): Don't send cookies unless
requested.
(url-http-parse-headers): Don't store cookies unless requested.
* url.el (url-retrieve): Ditto
* url-queue.el (url-queue-retrieve): Take an optional
`inhibit-cookies' parameter.
* url-parse.el (url): Add the `use-cookies' slot to the URL struct
to be able to keep track of whether to do cookies or not on a
per-URL basis.
* url-queue.el (url-queue-setup-runners): New function that uses
`run-with-idle-timer' for extra asynchronicity.
(url-queue-remove-jobs-from-host): New function.
(url-queue-callback-function): Remove jobs from the same host if
connection failed.
