Include zncconfig.h in all headers

The rule is that zncconfig.h must be the very same thing that is included. We
cheat and only include it in headers (so that modules dont have to have be
changed). However, it looks like some modules where missed.

This commit fixes test/ConfigTest which crashed if _GLIBCXX_DEBUG was enabled
(--enable-debug) because it didn't see this define before including a c++
header.

Signed-off-by: Uli Schlachter <psychon@znc.in>

Config.h

@@ -9,6 +9,7 @@
 #ifndef CONFIG_H
 #define CONFIG_H
 
+#include "zncconfig.h"
 #include "ZNCString.h"
 
 class CFile;

ExecSock.h

@@ -9,6 +9,7 @@
 #ifndef EXEC_SOCK_H
 #define EXEC_SOCK_H
 
+#include "zncconfig.h"
 #include "Socket.h"
 #include <signal.h>
 

ZNCDebug.h

@@ -9,6 +9,7 @@
 #ifndef ZNCDEBUG_H
 #define ZNCDEBUG_H
 
+#include "zncconfig.h"
 #include <iostream>
 
 using std::cout;