Log Message:
Update to 1.2.26:

version 1.2.26beta01 [February 21, 2008]
  Added missing "(" in pngmem.c.  Bug introduced in libpng-1.2.2/1.0.13

version 1.2.26beta02 [March 12, 2008]
  Refined error message returned from deflateInit2 in pngwutil.c
  Check IHDR length in png_push_read_chunk() before saving it.

version 1.2.26beta03 [March 16, 2008]
  Revised contrib/gregbook to handle premature end-of-file and file
    read errors correctly.

version 1.2.26beta04 [March 18, 2008]
  Free png_ptr->big_row_buf and png_ptr->prev_row before allocating
    new copies in png_read_start_row().  Bug introduced in libpng-1.2.22.

version 1.2.26beta05 [March 19, 2008]
  Removed extra png_free() added in libpng-1.2.26beta04.

version 1.2.26beta06 [March 19, 2008]
  Avoid reallocating big_row_buf and prev_row when the size does not increase.

version 1.2.26rc01 [April 2, 2008]
  Ifdef out some code that is unused when interlacing is not supported.