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

from the source files, along with "#define PNG_EXPOSE_INTERNAL_STRUCTURES"
and "#define PNG_NO_PEDANTIC_WARNINGS" (John Bowler).
Also created new pngdebug.h and moved debug definitions there.

and updated the "last change" comments to 1.5.0

and added "#define PNG_NO_PEDANTIC_WARNINGS" in the libpng source files.