kvp frame to template and correcting failure macro

The template avoids the need to cast to and from void*, and adds flexibility to
the targeted function's signature.

test-stuff.h defines a macro, "failure" which is used as an identifier
in the standard IO library, so I moved any inclusion of test-stuff.h to
the last include position so that "failure" wouldn't be defined before
the IO library was included.

libgnucash/engine/gnc-aqbanking-templates.cpp

@@ -30,9 +30,9 @@
 extern "C"
 {
 #include "gnc-aqbanking-templates.h"
-#include "qofinstance-p.h"
 }
 
+#include "qofinstance-p.h"
 #include "kvp-frame.hpp"
 #include "gnc-rational.hpp"