In all prior versions of libpng most configuration options
    controlled by compiler #defines had to be repeated by the
    application code that used libpng.  This patch changes this
    so that compilation options that can only be changed at build
    time are frozen in the build.  Options that are compiler
    dependent (and those that are system dependent) are evaluated
    each time - pngconf.h holds these.  Options that can be changed
    per-file in the application are in png.h.  Frozen options are
    in the new installed header file pnglconf.h

Removed the include of sys/types.h - apparently unnecessary now on the
  platforms on which it happened (all but Mac OS and RISC OS).
Moved the Mac OS test into pngpriv.h (the only place it is used.)

Removed scripting cruft from scripts/makefile.mingw
Removed mention of now nonexistent files from scripts/README.txt

updated projects/visualc71 and removed scripts/makefile.cygwin.

  and callbacks.
Changed rules for generation of the various symbol files and added a new
  rule for a DEF file (which is also added to the distribution).
Updated the symbol file generation to stop it adding spurious spaces
  to EOL (coming from preprocessor macro expansion).  Added a facility
  to join tokens in the output and rewrite *.dfn to use this.

    for DEF file generation.

    PNG_CALLBACK added to make callback definitions uniform.  PNGAPI split
    into PNGCAPI (base C form), PNGAPI (exports) and PNGCBAPI (callbacks),
    and appropriate changes made to all files.  Cygwin builds re-hinged to
    allow procedure call standard changes and to remove the need for the DEF
    file (fixes build on Cygwin).

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Glenn R-P

and removed a redundant line from the copyright info in pngconf.h

with the help of "cppi".

when building on AIX.

otherwise AIX reserves "jmpbuf" and renames it to "__jmpbuf".

from png.h