libpng: Upgrade to 1.6.25

The changes from 1.6.22 (beta) to
1.6.25 (final) include many general fixes,
fixes for memory leak issues and optimizations
in order to improve performance.
Also upstream added support for the MIPS
platform.

Support for Intel SSE isn't built in any more.
For support a patch in contrib/intel/intel_sse.patch
has to be applied. This patch additionally
documents this in README.android as an Android
specific addition.

The patch for Intel SSE support
from upstream applied cleanly.

Libpng 1.6.25 released on September 1, 2016.

Test: built for ARM and checked whether NEON optimizations were compiled
      built for x86/x86_64 and checked whether SSE optimizations were compiled

Change-Id: If647f42a1fb4d7022286010d262d287dac4030df
Signed-off-by: Alex Naidis <alex.naidis@linux.com>
diff --git a/pngstruct.h b/pngstruct.h
index c1f35ed..2b0eb49 100644
--- a/pngstruct.h
+++ b/pngstruct.h
@@ -1,8 +1,8 @@
 
 /* pngstruct.h - header file for PNG reference library
  *
- * Last changed in libpng 1.6.18 [July 23, 2015]
- * Copyright (c) 1998-2002,2004,2006-2015 Glenn Randers-Pehrson
+ * Last changed in libpng 1.6.24 [August 4, 2016]
+ * Copyright (c) 1998-2002,2004,2006-2016 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
@@ -249,7 +249,7 @@
    png_byte filter;           /* file filter type (always 0) */
    png_byte interlaced;       /* PNG_INTERLACE_NONE, PNG_INTERLACE_ADAM7 */
    png_byte pass;             /* current interlace pass (0 - 6) */
-   png_byte do_filter;        /* row filter flags (see PNG_FILTER_ below ) */
+   png_byte do_filter;        /* row filter flags (see PNG_FILTER_ in png.h ) */
    png_byte color_type;       /* color type of file */
    png_byte bit_depth;        /* bit depth of file */
    png_byte usr_bit_depth;    /* bit depth of users row: write only */