Log Message:
Update to 1.2.38:

version 1.2.38beta01 [June 17, 2009]
  Revised libpng*.txt and libpng.3 to mention calling png_set_IHDR()
    multiple times and to specify the sample order in the tRNS chunk,
    because the ISO PNG specification has a typo in the tRNS table.
  Changed several PNG_UNKNOWN_CHUNK_SUPPORTED to
    PNG_HANDLE_AS_UNKNOWN_SUPPORTED, to make the png_set_keep mechanism
    available for ignoring known chunks even when not saving unknown chunks.
  Adopted preference for consistent use of "#ifdef" and \ 
"#ifndef" versus
    "#if defined()" and "if !defined()" where possible.
  Added PNG_NO_HANDLE_AS_UNKNOWN in the PNG_LEGACY_SUPPORTED block of
    pngconf.h, and moved the various unknown chunk macro definitions
    outside of the PNG_READ|WRITE_ANCILLARY_CHUNK_SUPPORTED blocks.

version 1.2.38rc01 [June 24, 2009]
  No changes.

version 1.2.38rc02 [June 29, 2009]
  Added a reference to the libpng license in each source file.

version 1.2.38rc03 [July 11, 2009]
  Revised references to the libpng license in pngconf.h and contrib/visupng
    source files.
  Rebuilt configure scripts with autoconf-2.63.

version 1.0.47 and 1.2.38 [July 16, 2009]
  No changes.