merge r3452, r3462, r3471, r3472: fix miscellaneous name bugs: *) fix $upstream_http_ variable prefix length *) use a right "Location" header name, however, it did not harm, since ngx_http_variable_sent_location() never use key name field *) fix proxy_redirect name in error message *) "proxy_redirect default" may not be used if a proxy_pass uses variables

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