Log Message:
Update to 1.5.11:

Version 1.5.11beta01 [April 28, 2012]
  Revised scripts/makefile.darwin: use system zlib; remove quotes around
    architecture list; add missing ppc architecture; add architecture options
    to shared library link; don't try to create a shared lib based on missing
    RELEASE variable.
  Enable png_set_check_for_invalid_index() for both read and write.
  Removed #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED/#endif in pngpriv.h around
    declaration of png_handle_unknown().
  Added -lssp_nonshared in a comment in scripts/makefile.freebsd
    and changed deprecated NOOBJ and NOPROFILE to NO_OBJ and NO_PROFILE.

Version 1.5.11rc01 [May 23, 2012]
  No changes.

Version 1.5.11rc02 [May 29, 2012]
  Fixed some typos in comments.
  Revised CMakeLists.txt to not attempt to make a symlink under mingw.
  Added two images to contrib/pngsuite (1-bit and 2-bit transparent grayscale),
    and renamed three whose names were inconsistent with those in
    pngsuite/README.txt.

Version 1.5.11rc03 [June 4, 2012]
  Do not depend upon a GCC feature macro being available for use in generating
    the linker mapfile symbol prefix.
  Made fixes for new optimization warnings from gcc 4.7.0. The compiler
    performed an optimization which is safe but then warned about it.
    Changing the type of 'palette_number' in pngvalid.c removes the warning.

Version 1.5.11rc04 [June 6, 2012]
  Improved performance of new do_check_palette_indexes() function.

Version 1.5.11rc05 [June 7, 2012]
  Don't check palette indexes if num_palette is 0 (as it can be in MNG files).

Version 1.5.11 [June 14, 2012]
  Include zlib.h in contrib/gregbook and contrib/visupng examples.