Merge branch 'ap/http-redirect-wwwauth-fix' into seen

When cURL follows a redirect, the WWW-Authenticate headers from the
redirect target were lost because credential_from_url() cleared the
credential state. This has been fixed by preserving the collected
headers across the redirect update.

* ap/http-redirect-wwwauth-fix:
  http: preserve wwwauth_headers across redirects

diff --cc http.c
Simple merge

diff --cc t/t5563-simple-http-auth.sh
Simple merge