Fix all references to config.h

config.h is created in $(top_buildir)/config.h.
Let's make sure all CPPFLAGS add correct -Ipath includes,
and that all code includes the correct file.

Change-Id: Ie9ea38bb009bc715b01cde4d66d181f7bec2e7bd
diff --git a/src/core/it_q.c b/src/core/it_q.c
index fda6c1f..a3ff420 100644
--- a/src/core/it_q.c
+++ b/src/core/it_q.c
@@ -32,7 +32,7 @@
  * and call a queue-specific callback function.
  */
 
-#include "../config.h"
+#include "config.h"
 
 #ifdef HAVE_SYS_EVENTFD_H