gnunet_container_lib.h incompatible with C++ in GNUnet 0.19.0

[marty1885]

Hi,

Nice for releasing GNUnet 0.19.0. I've upgraded and find my C++ programs fails 
to compile against the new headers. After some debugging the root cause is a (I 
assume) failed attempt at completing removing `extern "C"` guards in 
`gnunet_container_lib.h`. Seems the top half of the guard is removed but the 
bottom half isn't. Leading to an error when including any headers that uses 
that file from C++. For example the following simple program fails to compile.

I have scanned through the GNUnet website and not sure how to contribute my 
fix. The "development tutorial" page 
(https://docs.gnunet.org/tutorial/tutorial.html) is broken on the website. The 
website also mentioned needing to sign copyright assignment? What exactly 
should I do?

#include <gnunet/gnunet_core_service.h>

int main()
{
    reutrn 0;
}

Compiling with g++ leads to the following error:

❯ g++ simple.cpp
In file included from simple.cpp:1:
/usr/include/gnunet/gnunet_core_service.h:440:1: error: expected declaration 
before ‘}’ token
  440 | }
      | ^

And following patch fixes it.

--- /usr/include/gnunet/gnunet_container_lib.h.old      2022-12-09 
00:29:44.746504181 +0800
+++ /usr/include/gnunet/gnunet_container_lib.h  2022-12-09 00:29:58.554055321 
+0800
@@ -2328,15 +2328,6 @@
 GNUNET_CONTAINER_heap_update_cost (struct GNUNET_CONTAINER_HeapNode *node,
                                    GNUNET_CONTAINER_HeapCostType new_cost);
 
-
-#if 0 /* keep Emacsens' auto-indent happy */
-{
-#endif
-#ifdef __cplusplus
-}
-#endif
-
-
 /* ifndef GNUNET_CONTAINER_LIB_H */
 #endif
 
Best,
Martin