Fix building with gcc-4.7

https://bugs.gentoo.org/show_bug.cgi?id=419165
--- a/config.h
+++ b/config.h
@@ -129,7 +129,7 @@
                 if (!isempty(s)) {
                    T *l = new T;
                    if (l->Parse(s))
-                      Add(l);
+                      this->Add(l);
                    else {
                       esyslog("ERROR: error in %s, line %d", fileName, line);
                       delete l;