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.

extern/libpng/include/scripts/libpng-config-head.in

@@ -1,24 +1,24 @@
-#! /bin/sh
-
-# libpng-config
-# provides configuration info for libpng.
-
-# Copyright (C) 2002 Glenn Randers-Pehrson
-
-# This code is released under the libpng license.
-# For conditions of distribution and use, see the disclaimer
-# and license in png.h
-
-# Modeled after libxml-config.
-
-version=1.5.1
-prefix=""
-libdir=""
-libs=""
-I_opts=""
-L_opts=""
-R_opts=""
-cppflags=""
-ccopts=""
-ldopts=""
-
+#! /bin/sh
+
+# libpng-config
+# provides configuration info for libpng.
+
+# Copyright (C) 2002 Glenn Randers-Pehrson
+
+# This code is released under the libpng license.
+# For conditions of distribution and use, see the disclaimer
+# and license in png.h
+
+# Modeled after libxml-config.
+
+version=1.5.10
+prefix=""
+libdir=""
+libs=""
+I_opts=""
+L_opts=""
+R_opts=""
+cppflags=""
+ccopts=""
+ldopts=""
+