bug#7908: png-1.5 fix for emacs-23.2 and HEAD

[Chong Yidong]

Andreas Schwab <schwab@linux-m68k.org> writes:

>> Aha, I think it makes sense.  Since DEF_IMGLIB_FN defines a return type
>> of int, whereas fn_png_set_longjmp_fn actually returns a (jmp_buf *), we
>> do indeed need to perform the extra cast.
>
> You can't expect this to work, though.

Hmm, true.  So maybe something like this instead?

*** src/image.c 2011-01-29 21:28:26 +0000
--- src/image.c 2011-01-29 22:26:51 +0000
***************
*** 5592,5598 ****
  
  #if (PNG_LIBPNG_VER >= 10500)
  DEF_IMGLIB_FN (png_longjmp);
! DEF_IMGLIB_FN (png_set_longjmp_fn);
  #endif /* libpng version >= 1.5 */
  
  static int
--- 5592,5598 ----
  
  #if (PNG_LIBPNG_VER >= 10500)
  DEF_IMGLIB_FN (png_longjmp);
! jmp_buf* (FAR CDECL *fn_png_set_longjmp_fn);
  #endif /* libpng version >= 1.5 */
  
  static int