Log Message:
Update png to 1.5.7:

Changes since the last public release (1.5.6):
  Added support for ARM processor (Mans Rullgard)
  Fixed bug in pngvalid on early allocation failure; fixed type cast in
    pngmem.c; pngvalid would attempt to call png_error() if the allocation
    of a png_struct or png_info failed. This would probably have led to a
    crash.  The pngmem.c implementation of png_malloc() included a cast
    to png_size_t which would fail on large allocations on 16-bit systems.
  Fix for the preprocessor of the Intel C compiler. The preprocessor
    splits adjacent @ signs with a space; this changes the concatentation
    token from @-@-@ to PNG_JOIN; that should work with all compiler
    preprocessors.
  Paeth filter speed improvements from work by Siarhei Siamashka. This
    changes the 'Paeth' reconstruction function to improve the GCC code
    generation on x86. The changes are only part of the suggested ones;
    just the changes that definitely improve speed and remain simple.
    The changes also slightly increase the clarity of the code.
  Check compression_type parameter in png_get_iCCP and remove spurious
    casts. The compression_type parameter is always assigned to, so must
    be non-NULL. The cast of the profile length potentially truncated the
    value unnecessarily on a 16-bit int system, so the cast of the (byte)
    compression type to (int) is specified by ANSI-C anyway.
  Fixed FP division by zero in pngvalid.c; the 'test_pixel' code left
    the sBIT fields in the test pixel as 0, which resulted in a floating
    point division by zero which was irrelevant but causes systems where
    FP exceptions cause a crash. Added code to pngvalid to turn on FP
    exceptions if the appropriate glibc support is there to ensure this is
    tested in the future.
  Added versioning to pnglibconf.h comments.
  Installed more accurate linear to sRGB conversion tables. The slightly
    modified tables reduce the number of 16-bit values that
    convert to an off-by-one 8-bit value.  The "makesRGB.c" code that \ 
was used
    to generate the tables is now in a contrib/sRGBtables sub-directory.
  Added run-time detection of NEON support.
  Multiple transform bug fixes plus a work-round for double gamma correction.
    libpng does not support more than one transform that requires linear data
    at once - if this is tried typically the results is double gamma
    correction. Since the simplified APIs can need rgb to gray combined with
    a compose operation it is necessary to do one of these outside the main
    libpng transform code. This check-in also contains fixes to various bugs
    in compose and rgb to gray (on palette).
  Fixes for C++ compilation using g++ When libpng source is compiled
    using g++. The compiler imposes C++ rules on the C source; thus it
    is desireable to make the source work with either C or C++ rules
    without throwing away useful error information.  This change adds
    png_voidcast to allow C semantic (void*) cases or the corresponding
    C++ static_cast operation, as appropriate.
  Added --noexecstack to assembler file compilation. GCC does not set
    this on assembler compilation, even though it does on C compilation.
    This creates security issues if assembler code is enabled; the
    work-around is to set it by default in the flags for $(CCAS)
  Removed "zTXt" from warning in generic chunk decompression function.
  Validate time settings passed to pngset() and png_convert_to_rfc1123()
    (Frank Busse).
  Added MINGW support to CMakeLists.txt
  Reject invalid compression flag or method when reading the iTXt chunk.
  Moved pngvalid.c into contrib/libtests
  Rebuilt Makefile.in, configure, etc., with autoconf-2.68
  Replaced an "#if" with "#ifdef" in pngrtran.c
  Revised #if PNG_DO_BC block in png.c (use #ifdef and add #else)
  Revised pngconf.h to use " __declspec(restrict)" only when MSC_VER \ 
>= 1400,
    as in libpng-1.5.4.
  Put CRLF line endings in the owatcom project files.
  Updated CMakeLists.txt to account for the relocation of pngvalid.c
  Minor fixes to pngvalid.c for gcc 4.6.2 compatibility to remove warnings
    reported by earlier versions.