Update to 1.2.24:

version 1.2.24beta01 [November 19, 2007]
  Moved misplaced test for malloc failure in png_set_sPLT().  This bug was
    introduced in libpng-1.2.20beta01.
  Ifdef out avg_row etc from png.h and pngwrite.c when PNG_NO_WRITE_FILTER
  Do not use png_ptr->free_fn and png_ptr->mem_fn in png_destroy_read_struct()
    when png_ptr is NULL (Marshall Clow).
  Updated handling of symbol prefixes in Makefile.am and configure.ac (Mike
    Frysinger).

version 1.2.24beta02 [November 30, 2007]
  Removed a useless test and fixed incorrect test in png_set_cHRM_fixed()
    (David Hill).

version 1.2.24rc01 [December 7, 2007]
  No changes.

version 1.2.24    [December 14, 2007]
  Make sure not to redefine _BSD_SOURCE in pngconf.h
  Revised gather.sh and makefile.std in contrib/pngminim to avoid compiling
    unused files.

(wiz)