This is necessary when libz is upgraded to 1.2.4

and CMakeLists.txt, and changed the name of png_ptr->jmpbuf in pngstruct.h
to png_ptr->png_jmpbuf.

when building on AIX.

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

too break from "while" and issue a png_warning on over limit.

Removed unused "buffer_size" variable from png_decompress_chunk().

and updated the "last change" comments to 1.5.0

and undid the linewrapping that it required.
Revised comments in pngstruct.h and pnginfo.h and added pointers to
the libpng license.

from png.h

    in pngtest.c