allow to proxy_pass_header/fastcgi_pass_header "X-Accel-Redirect",
"X-Accel-Limit-Rate", "X-Accel-Buffering", and "X-Accel-Charset"

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index cc303b4..e370196 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -224,19 +224,19 @@
     { ngx_string("X-Accel-Redirect"),
                  ngx_http_upstream_process_header_line,
                  offsetof(ngx_http_upstream_headers_in_t, x_accel_redirect),
-                 ngx_http_upstream_ignore_header_line, 0, 0 },
+                 ngx_http_upstream_copy_header_line, 0, 0 },
 
     { ngx_string("X-Accel-Limit-Rate"),
                  ngx_http_upstream_process_limit_rate, 0,
-                 ngx_http_upstream_ignore_header_line, 0, 0 },
+                 ngx_http_upstream_copy_header_line, 0, 0 },
 
     { ngx_string("X-Accel-Buffering"),
                  ngx_http_upstream_process_buffering, 0,
-                 ngx_http_upstream_ignore_header_line, 0, 0 },
+                 ngx_http_upstream_copy_header_line, 0, 0 },
 
     { ngx_string("X-Accel-Charset"),
                  ngx_http_upstream_process_charset, 0,
-                 ngx_http_upstream_ignore_header_line, 0, 0 },
+                 ngx_http_upstream_copy_header_line, 0, 0 },
 
 #if (NGX_HTTP_GZIP)
     { ngx_string("Content-Encoding"),