third_party/libpng: update to 1.2.54

third_party/libpng/README

-README for libpng version 1.2.52 - November 20, 2014 (shared library 12.0)
+README for libpng version 1.2.54 - November 12, 2015 (shared library 12.0)
 See the note about version numbers near the top of png.h
 
 See INSTALL for instructions on how to install libpng.
 
 Libpng comes in several distribution formats.  Get libpng-*.tar.gz,
 libpng-*.tar.xz, or libpng-*.tar.bz2 if you want UNIX-style line
 endings in the text files, or lpng*.7z or lpng*.zip if you want DOS-style
 line endings.  You can get UNIX-style line endings from the *.zip file
 by using "unzip -a" but there seems to be no simple way to recover
 UNIX-style line endings from the *.7z file.  The *.tar.xz file is
@@ skipping 116 matching lines @@
 https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
 subscribe). On the other hand, please do not send libpng questions to
 that address, send them to me or to the png-mng-implement list.  I'll
 get them in the end anyway.  If you have a question about something
 in the PNG specification that is related to using libpng, send it
 to me.  Send me any questions that start with "I was using libpng,
 and ...".  If in doubt, send questions to me.  I'll bounce them
 to others, if necessary.
 
 Please do not send suggestions on how to change PNG.  We have
-been discussing PNG for nineteen years now, and it is official and
+been discussing PNG for twenty years now, and it is official and
 finished.  If you have suggestions for libpng, however, I'll
 gladly listen.  Even if your suggestion is not used immediately,
 it may be used later.
 
 Files in this distribution:
 
       ANNOUNCE      =>  Announcement of this version, with recent changes
       CHANGES       =>  Description of changes between libpng versions
       KNOWNBUG      =>  List of known bugs and deficiencies
       LICENSE       =>  License to use and redistribute libpng
@@ skipping 51 matching lines @@
        wince.txt        =>  Contains instructions for downloading a
                             Microsoft Visual C++ (Windows CD Toolkit)
                             workspace for building libpng and zlib on
                             WindowsCE
        xcode            =>  Contains xcode project files
       scripts       =>  Directory containing scripts for building libpng:
        descrip.mms      =>  VMS makefile for MMS or MMK
        makefile.std     =>  Generic UNIX makefile (cc, creates static
                             libpng.a)
        makefile.elf     =>  Linux/ELF gcc makefile symbol versioning,
-                            creates libpng12.so.0.1.2.52)
+                            creates libpng12.so.0.1.2.54)
        makefile.linux   =>  Linux/ELF makefile (gcc, creates
-                            libpng12.so.0.1.2.52)
+                            libpng12.so.0.1.2.54)
        makefile.gcmmx   =>  Linux/ELF makefile (gcc, creates
-                            libpng12.so.0.1.2.52, previously
+                            libpng12.so.0.1.2.54, previously
                             used assembler code tuned for Intel MMX
                             platform)
        makefile.gcc     =>  Generic makefile (gcc, creates static
                             libpng.a)
        makefile.knr     =>  Archaic UNIX Makefile that converts files
                             with ansi2knr (Requires ansi2knr.c from
                             ftp://ftp.cs.wisc.edu/ghost)
        makefile.aix     =>  AIX makefile
        makefile.cygwin  =>  Cygwin/gcc makefile
        makefile.darwin  =>  Darwin makefile
        makefile.dec     =>  DEC Alpha UNIX makefile
        makefile.freebsd =>  FreeBSD makefile
        makefile.hpgcc   =>  HPUX makefile using gcc
        makefile.hpux    =>  HPUX (10.20 and 11.00) makefile
        makefile.hp64    =>  HPUX (10.20 and 11.00) makefile, 64 bit
        makefile.ibmc    =>  IBM C/C++ version 3.x for Win32 and OS/2
                             (static)
        makefile.intel   =>  Intel C/C++ version 4.0 and later
        libpng.icc       =>  Project file, IBM VisualAge/C++ 4.0 or later
        makefile.netbsd  =>  NetBSD/cc makefile, makes libpng.so.
        makefile.ne12bsd  =>  NetBSD/cc makefile, makes libpng12.so
        makefile.openbsd =>  OpenBSD makefile
        makefile.sgi     =>  Silicon Graphics IRIX (cc, creates static lib)
        makefile.sggcc   =>  Silicon Graphics
-                            (gcc, creates libpng12.so.0.1.2.52)
+                            (gcc, creates libpng12.so.0.1.2.54)
        makefile.sunos   =>  Sun makefile
        makefile.solaris =>  Solaris 2.X makefile
-                            (gcc, creates libpng12.so.0.1.2.52)
+                            (gcc, creates libpng12.so.0.1.2.54)
        makefile.so9     =>  Solaris 9 makefile
-                            (gcc, creates libpng12.so.0.1.2.52)
+                            (gcc, creates libpng12.so.0.1.2.54)
        makefile.32sunu  =>  Sun Ultra 32-bit makefile
        makefile.64sunu  =>  Sun Ultra 64-bit makefile
        makefile.sco     =>  For SCO OSr5  ELF and Unixware 7 with Native cc
        makefile.mips    =>  MIPS makefile
        makefile.acorn   =>  Acorn makefile
        makefile.amiga   =>  Amiga makefile
        smakefile.ppc    =>  AMIGA smakefile for SAS C V6.58/7.00 PPC
                             compiler (Requires SCOPTIONS, copied from
                             scripts/SCOPTIONS.ppc)
        makefile.atari   =>  Atari makefile
@@ skipping 19 matching lines @@
 -Glenn Randers-Pehrson (current maintainer, since 1998)
  Internet: glennrp at users.sourceforge.net
 
 -Andreas Eric Dilger (former maintainer, 1996-1997)
  Internet: adilger at enel.ucalgary.ca
  Web: http://members.shaw.ca/adilger/
 
 -Guy Eric Schalnat (original author and former maintainer, 1995-1996)
  (formerly of Group 42, Inc)
  Internet: gschal at infinet.com