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/config.h.in

@@ -3,6 +3,9 @@
 /* Define to 1 if you have the <dlfcn.h> header file. */
 #undef HAVE_DLFCN_H
 
+/* Define to 1 if you have the `feenableexcept' function. */
+#undef HAVE_FEENABLEEXCEPT
+
 /* Define to 1 if you have the <inttypes.h> header file. */
 #undef HAVE_INTTYPES_H
 
@@ -70,6 +73,12 @@
 /* Define to the version of this package. */
 #undef PACKAGE_VERSION
 
+/* Align row buffers */
+#undef PNG_ALIGNED_MEMORY_SUPPORTED
+
+/* Enable ARM NEON optimizations */
+#undef PNG_ARM_NEON
+
 /* Define to 1 if you have the ANSI C header files. */
 #undef STDC_HEADERS
 
@@ -82,5 +91,19 @@
 /* Define to empty if `const' does not conform to ANSI C. */
 #undef const
 
+/* Define to the equivalent of the C99 'restrict' keyword, or to
+   nothing if this is not supported.  Do not define if restrict is
+   supported directly.  */
+#undef restrict
+/* Work around a bug in Sun C++: it does not support _Restrict or
+   __restrict__, even though the corresponding Sun C compiler ends up with
+   "#define restrict _Restrict" or "#define restrict __restrict__" in the
+   previous line.  Perhaps some future version of Sun C++ will work with
+   restrict; if so, hopefully it defines __RESTRICT like Sun C does.  */
+#if defined __SUNPRO_CC && !defined __RESTRICT
+# define _Restrict
+# define __restrict__
+#endif
+
 /* Define to `unsigned int' if <sys/types.h> does not define. */
 #undef size_t