Give props to Martin Pool

Martin Pool was the original author of the code referenced in the clone
example. Make note that he's given his permission and also give him the
proper credit.

examples/network/clone.c

@@ -9,7 +9,10 @@
 # include <unistd.h>
 #endif
 
-/* Shamelessly borrowed from http://stackoverflow.com/questions/3417837/ */
+/* Shamelessly borrowed from http://stackoverflow.com/questions/3417837/
+ * with permission of the original author, Martin Pool.
+ * http://sourcefrog.net/weblog/software/languages/C/unused.html
+ */
 #ifdef UNUSED
 #elif defined(__GNUC__)
 # define UNUSED(x) UNUSED_ ## x __attribute__((unused))