Log Message:
Update to 1.6.15:

Version 1.6.15beta01 [October 29, 2014]
  Changed "if (!x)" to "if (x == 0)" and "if (x)" \ 
to "if (x != 0)"
  Simplified png_free_data().
  Added missing "ptr = NULL" after some instances of png_free().

Version 1.6.15beta02 [November 1, 2014]
  Changed remaining "if (!x)" to "if (x == 0)" and "if \ 
(x)" to "if (x != 0)"

Version 1.6.15beta03 [November 3, 2014]
  Added PNG_USE_ARM_NEON configuration flag (Marcin Juszkiewicz).

Version 1.6.15beta04 [November 4, 2014]
  Removed new PNG_USE_ARM_NEON configuration flag and made a one-line
    revision to configure.ac to support ARM on aarch64 instead (John Bowler).

Version 1.6.15beta05 [November 5, 2014]
  Use png_get_libpng_ver(NULL) instead of PNG_LIBPNG_VER_STRING in
    example.c, pngtest.c, and applications in the contrib directory.
  Avoid out-of-bounds memory access in png_user_version_check().
  Simplified and future-proofed png_user_version_check().
  Fixed GCC unsigned int->float warnings. Various versions of GCC
    seem to generate warnings when an unsigned value is implicitly
    converted to double. This is probably a GCC bug but this change
    avoids the issue by explicitly converting to (int) where safe.
  Free all allocated memory in pngimage. The file buffer cache was left
    allocated at the end of the program, harmless but it causes memory
    leak reports from clang.
  Fixed array size calculations to avoid warnings. At various points
    in the code the number of elements in an array is calculated using
    sizeof.  This generates a compile time constant of type (size_t) which
    is then typically assigned to an (unsigned int) or (int). Some versions
    of GCC on 64-bit systems warn about the apparent narrowing, even though
    the same compiler does apparently generate the correct, in-range,
    numeric constant.  This adds appropriate, safe, casts to make the
    warnings go away.

Version 1.6.15beta06 [November 6, 2014]
  Reverted use png_get_libpng_ver(NULL) instead of PNG_LIBPNG_VER_STRING
    in the manual, example.c, pngtest.c, and applications in the contrib
    directory.  It was incorrect advice.

Version 1.6.15beta07 [November 7, 2014]
  Removed #ifdef PNG_16BIT_SUPPORTED/#endif around png_product2(); it is
    needed by png_reciprocal2().
  Added #ifdef PNG_16BIT_SUPPORTED/#endif around png_log16bit() and
    png_do_swap().
  Changed all "#endif /* PNG_FEATURE_SUPPORTED */" to "#endif /* \ 
FEATURE */"

Version 1.6.15beta08 [November 8, 2014]
  More housecleaning in *.h

Version 1.6.15rc01 [November 13, 2014]

Version 1.6.15rc02 [November 14, 2014]
  The macros passed in the command line to Borland make were ignored if
    similarly-named macros were already defined in makefiles. This behavior
    is different from POSIX make and other make programs.  Surround the
    macro definitions with ifndef guards (Cosmin).

Version 1.6.15rc03 [November 16, 2014]
  Added "-D_CRT_SECURE_NO_WARNINGS" to CFLAGS in scripts/makefile.vcwin32.
  Removed the obsolete $ARCH variable from scripts/makefile.darwin.

Version 1.6.15 [November 20, 2014]
  No changes.