add warnings for proxy_no_cache and fastcgi_no_cache

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 2fff21c..b067d60 100644
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -1916,6 +1916,12 @@
     ngx_conf_merge_ptr_value(conf->upstream.no_cache,
                              prev->upstream.no_cache, NULL);
 
+    if (conf->upstream.no_cache && conf->upstream.cache_bypass == NULL) {
+        ngx_log_error(NGX_LOG_WARN, cf->log, 0,
+             "\"proxy_no_cache\" functionality has been changed in 0.8.46, "
+             "now it should be used together with \"proxy_cache_bypass\"");
+    }
+
     ngx_conf_merge_ptr_value(conf->upstream.cache_valid,
                              prev->upstream.cache_valid, NULL);