[libpng17] Imported from libpng-1.7.0beta27.tar
[libpng17] Bump version to 1.7.0beta28
[libpng17] Fix typo in CHANGES and ANNOUNCE
[libpng17] Updated scripts/makefile.* to use CPPFLAGS (Cosmin)
[libpng17] Added clang attribute support (Cosmin).
[libpng17] Correct a comment in pngconf.h
[libpng17] Checked in clang attribute support.