[libpng16] Imported from libpng-1.6.7.tar
[libpng16] Update version number in CHANGES file.
[libpng16] Update version number in manual and png.h
[libpng16] Bump version to 1.6.8beta01
[libpng16] Added #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED/#endif in pngpread.c
[libpng16] Reduced scope of recently-added #ifdef block

(#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED/#endif in pngpread.c)
[libpng16] Changed ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED to

ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTE in pngpread.c to agree with
what is in pngpriv.h
[libpng16] Moved prototype for png_handle_unknown() in pngpriv.h outside of

the #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED/#endif block.
Removed recently-added #ifdef from pngpread.c; moving the prototype
in pngpriv.h fixed the compiler warning that the #ifdef was trying
to solve.
[libpng16] Added "-Wall" to CFLAGS in contrib/pngminim/*/makefile
[libpng16] Reverted change of ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED

to PNG_SET_UNKNOWN_SUPPORTED in pngpread.c; it led to the possibility of
calling png_handle_unknown() twice.
[libpng16] Conditionally compile some unused functions reported by -Wall

in pngminim.
[libpng16] Fixed 'minimal' builds. Various obviously useful minimal

configurations don't build because of missing contrib/libtests test programs
and overly complex dependencies in scripts/pnglibconf.dfa. This change adds
contrib/conftest/*.dfa files that can be used in automatic build
scripts to ensure that these configurations continue to build.
[libpng16] Enabled WRITE_INVERT and WRITE_PACK in contrib/pngminim/encoder.
[libpng16] Update contrib/tools/pngfix.c
[libpng16] Updated "last changed" dates
[libpng16] Fixed pngvalid 'fail' function declaration on the Intel C Compiler.

This reverts to the previous 'static' implementation and works round
the 'unused static function' warning by using PNG_UNUSED().
[libpng16] Avoid a clang scanner warning in pngfix.c
[libpng16] Added another "assert()" in pngfix.c
[libpng16] Imported from libpng-1.6.8beta01.tar
[libpng16] Bump version to 1.6.8beta02