merge r2950, r2951:

cache related fixes:

*) fix building --without-http-cache, broken in r2945
*) fix ./configure error message

auto/lib/md5/conf

@@ -100,9 +100,9 @@ cat << END
 
 $0: error: the HTTP cache module requires md5 functions
 from OpenSSL library.  You can either disable the module by using
---without-http_cache option, or install the OpenSSL library into the system,
+--without-http-cache option, or install the OpenSSL library into the system,
 or build the OpenSSL library statically from the source with nginx by using
---with-openssl=<path> option.
+--with-http_ssl_module --with-openssl=<path> options.
 
 END
             exit 1

src/http/modules/ngx_http_proxy_module.c

@@ -2343,7 +2343,10 @@ ngx_http_proxy_merge_headers(ngx_conf_t *cf, ngx_http_proxy_loc_conf_t *conf,
     }
 
     if (conf->headers_set_hash.buckets
-        && ((conf->upstream.cache == NULL) == (prev->upstream.cache == NULL)))
+#if (NGX_HTTP_CACHE)
+        && ((conf->upstream.cache == NULL) == (prev->upstream.cache == NULL))
+#endif
+       )
     {
         return NGX_OK;
     }

src/http/ngx_http_upstream.c

@@ -4086,7 +4086,10 @@ ngx_http_upstream_hide_headers_hash(ngx_conf_t *cf,
         conf->hide_headers_hash = prev->hide_headers_hash;
 
         if (conf->hide_headers_hash.buckets
-            && ((conf->cache == NULL) == (prev->cache == NULL)))
+#if (NGX_HTTP_CACHE)
+            && ((conf->cache == NULL) == (prev->cache == NULL))
+#endif
+           )
         {
             return NGX_OK;
         }