mod_proxy: ap_proxy_create_hdrbrgd() to clear hop-by-hop first and fixup last.

So that ap_proxy_clear_connection() runs on the original headers only and
proxy_run_fixups() on the final ones.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1901461 13f79535-47bb-0310-9956-ffa450edef68
