add a Request::raw_post buffer

This buffer is used when a Function::NeedToCopyRawPost() method returned true.

while here:
- remove WINIX_POST_PARAMS and WINIX_RAW_POST_STRING plugin messages

winixd/core/request.cpp

@@ -264,6 +264,7 @@ void Request::Clear()
 	cookie_id_string.clear();
 	send_data_buf.clear();
 	http_header_name.clear();
+	raw_post.clear();
 }