cpoll_cppsp: added plaintext benchmark

cpoll_cppsp/benchmark_config

@@ -4,6 +4,7 @@
     "default": {
       "setup_file": "setup",
       "json_url": "/json",
+	"plaintext_url": "/plaintext",
       "port": 16969,
       "sort": 115
     },

cpoll_cppsp/www/plaintext

@@ -0,0 +1,5 @@
+<%
+response->headers["Server"]="cppsp/0.2";
+response->headers["Content-Type"]="text/plain";
+%>Hello, World!
+