Log Message:
update to 1.2.6 (first official release after the recent
 security fixes)
changes:
version 1.2.6rc3 [August 9, 2004]
  Eliminated use of "abs()" in testing cHRM and gAMA values, to avoid
  trouble with some 64-bit compilers.  Created PNG_OUT_OF_RANGE() macro.
  Revised documentation of png_set_keep_unknown_chunks().
  Check handle_as_unknown status in pngpread.c, as in pngread.c previously.
  Moved  "PNG_HANDLE_CHUNK_*" macros out of PNG_INTERNAL section of png.h
  Added "rim" definitions for CONST4 and CONST6 in pnggccrd.c
version 1.2.6rc4 [August 10, 2004]
  Fixed mistake in pngtest.c introduced in 1.2.6rc2 (declaration of
  "pinfo" was out of place).
version 1.2.6rc5 [August 10, 2004]
  Moved  "PNG_HANDLE_CHUNK_*" macros out of PNG_ASSEMBLER_CODE_SUPPORTED
  section of png.h where they were inadvertently placed in version rc3.
version 1.2.6rc6 [August 15, 2004]
  Revised pngtest so memory allocation testing is only done when PNG_DEBUG==1.