Log Message:
Update to 1.2.23:

version 1.2.23beta01 [October 15, 2007]
  Reduced number of invocations of png_strlen() in pngset.c.
  Changed [azAZ09_] to [_abcde...89] in Makefile.am for better localization.

version 1.2.23beta02 [October 16, 2007]
  Eliminated png_strncpy() and png_strcpy() (Pierre Poissinger)
  Changed $AN to $(AN) in Makefile.am.

version 1.2.23beta03 [October 16, 2007]
  Fixed off-by-one error in pngset.c
  Restore statement to set last character of buffer to \0 in pngerror.c

version 1.2.23beta04 [October 23, 2007]
  Reject attempt to set all-zero cHRM values.

version 1.2.23beta05 [October 26, 2007]
  Add missing quotes in projects/visualc6, lost in version 1.2.20rc3

version 1.2.23rc01 [November 2, 2007]
  No changes.

version 1.2.23 [November 6, 2007]
  No changes.