The changes include support for function attributes in VC in addition to
    those already present in GCC - necessary because without these some
    warnings are unavoidable.  Fixes include signed/unsigned fixes in
    pngvalid and checks with gcc -Wall -Wextra -Wunused.
  VC requires function attributes on function definitions as well as
    declarations, PNG_FUNCTION has been added to enable this and the
    relevant function definitions changed.

that were recently introduced, mostly resulting from
safe but uncast assignments to shorter integers.  Also added a zlib
VStudio release library project because the latest zlib Official Windows
build does not include such a thing.

Renamed "png_sucker" to "png_store" in pngvalid.c

Also png_set_filter_heuristics_fixed and png_get_aspect_ratio_fixed.

  Fixed point APIs are now supported throughout (no missing APIs).
  Internal fixed point arithmetic support exists for all internal floating
    point operations.
  sCAL validates the floating point strings it is passed.
  Safe, albeit rudimentary, Watcom support is provided by PNG_API_RULE==2
  Two new APIs exist to get the number of passes without turning on the
    PNG_INTERLACE transform and to get the number of rows in the current
    pass.
  A new test program, pngvalid.c, validates the gamma code.
  Errors in the 16 bit gamma correction (overflows) have been corrected.
  cHRM chunk testing is done consistently (previously the floating point
    API bypassed it, because the test really didn't work on FP, now the test
    is performed on the actual values to be stored in the PNG file so it
    works in the FP case too.)
  Most floating point APIs now simply call the fixed point APIs after
    converting the values to the fixed point form used in the PNG file.
  The standard headers no longer include zlib.h, which is currently only
    required for pngstruct.h and can therefore be internal.
  (Patches by John Bowler)

"#ifdef" blocks in pngconf.h

Changed "extern" to "PNG_EXTERN" in pngpriv.h (except for the 'extern "C" {')