graphics/apngdis: #include <cstring>

This is fallout from png upgrade.  Modern GCC needs <cstring> for memcpy,
although clang seems to be happy without it.

graphics/apngdis/files/patch-apngdis.cpp

@@ -0,0 +1,10 @@
+--- apngdis.cpp.orig	2015-01-03 02:18:00 UTC
++++ apngdis.cpp
+@@ -30,6 +30,7 @@
+ #include <stdio.h>
+ #include <stdlib.h>
+ #include <vector>
++#include <cstring>
+ #include "png.h"     /* original (unpatched) libpng is ok */
+ #include "zlib.h"
+ using namespace std;