update libpng to 1.5.10, add precompiled library for ffmpeg 0.10.2 for mac, and Xcode 4.3 project in a separate project.

This should make it possible to build StepMania 5 on Mac OS X.
The catch is that it will only work with Snow Leopard and up, but I think this is better than nothing.

We can support PowerPC / 10.4-10.5 again when someone can make the old Xcode 3 project work.

Xcode/ffmpeg/include/libavcodec/opt.h

@@ -0,0 +1,34 @@
+/*
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * This header is provided for compatibility only and will be removed
+ * on next major bump
+ */
+
+#ifndef AVCODEC_OPT_H
+#define AVCODEC_OPT_H
+
+#include "libavcodec/version.h"
+
+#if FF_API_OPT_H
+#include "libavutil/opt.h"
+#endif
+
+#endif /* AVCODEC_OPT_H */