Merge of r4770: hide_headers/pass_headers inheritance fix.

Merge of r4770: hide_headers/pass_headers inheritance fix.

Hide headers and pass headers arrays might not be inherited correctly
into a nested location, e.g. in configuration like

    server {
        proxy_hide_header X-Foo;
        location / {
            location /nested/ {
                proxy_pass_header X-Pad;
            }
        }
    }

the X-Foo header wasn't hidden in the location /nested/.

Reported by Konstantin Svist,
http://mailman.nginx.org/pipermail/nginx-ru/2012-July/047555.html