to avoid "shadow" warnings.  Revised png_fixed() in png.c to avoid compiler
warning about reaching the end without returning anything.

if they need access to anything in zlib.h, and that a number of
macros such as png_memset() are no longer accessible by applications.

from png_charpp to png_bytepp in png_get_iCCP().  This change happened
in version 1.5.0beta36 but is not noted in the CHANGES.  Also, revised
the "synopsis" for png_get_iCCP() in libpng.3 accordingly.

(libpng14 => libpng15) (Cosmin)

(it was looking for the flag in png_ptr->transformations instead of in
png_ptr->flags).