Mostly this makes set_cookie more complex, as it now distinguishes
between HEADER_PARAM_NOT_FOUND and HEADER_PARAM_OUT_OF_MEMORY, and kills the cookie in the
latter case. However, the cookie->secure check became simpler.
Its return value is now an enum that lets callers know whether an
error occurred. However, this commit changes the callers only
minimally, so they do not yet check the return value.
src/cookies/dialogs.c (set_server): Set up a struct cookie and pass it
to accept_cookie, instead of calling set_cookie which might ask the user
to confirm. (This change also removes a dubious use of struct uri.)
src/cookies/cookies.c (get_cookie_server): No longer static.
src/cookies/cookies.h (get_cookie_server): Declare.
