Improve progname detection portability

`getprogname()` of FreeBSD is based on NetBSD's one, no reason to
prevent using it on NetBSD.
glibc also has own special variable for progname.

Signed-off-by: OBATA Akio <obache@wizdas.com>
(cherry picked from commit 965a808b91)

kio/kio/connection.cpp

@@ -42,8 +42,10 @@
 #include <kdebug.h>
 #include <tqsocketnotifier.h>
 
-#if defined(__OpenBSD__) || defined(__FreeBSD__)
+#if defined(__OpenBSD__) || defined(__FreeBSD__) || defined(__NetBSD__)
 #define __progname getprogname()
+#elif defined(_GNU_SOURCE) && defined(__GLIBC__)
+#define __progname program_invocation_short_name
 #else
 extern char *__progname;
 #endif