Proxy: better error message about unexpected data.

Requested by Igor Sysoev.

src/http/modules/ngx_http_proxy_module.c

diff --git a/src/http/modules/ngx_http_proxy_module.c b/src/http/modules/ngx_http_proxy_module.c
index 541c59f..12a54c7 100644
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -1614,7 +1614,8 @@
         p->upstream_done = 1;
 
         ngx_log_error(NGX_LOG_WARN, r->connection->log, 0,
-                      "upstream sent too much data");
+                      "upstream sent more data than specified in "
+                      "\"Content-Length\" header");
     }
 
     return NGX_OK;