[libpng17] Added #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED/#endif in pngpread.c
[libpng17] Moved prototype for png_handle_unknown() in pngpriv.h outside of

the #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED/#endif block.
[libpng17] Added "-Wall" to CFLAGS in contrib/pngminim/*/makefile
[libpng17] Ported recent changes from libpng16 to libpng17

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.
Enabled WRITE_INVERT and WRITE_PACK in contrib/pngminim/encoder.
[libpng17] Revert recent change to pngvalid.c.
[libpng17] Finished merging with libpng16 (pngrutil.c and pnglibconf.dfa)
[libpng17] Added an "assert()" to pngfix.c to quiet a clang scanner warning.
[libpng17] Added another "assert()" to pngfix.c
[libpng17] Imported from libpng-1.7.0beta23.tar
[libpng17] Bump version to 1.7.0beta24
[libpng17] Updated CHANGES and ANNOUNCE
[libpng17] Revised manual about handling of zlib CMF
[libpng17] Removed or marked PNG_UNUSED some harmless "dead assignments"

reported by clang scan-build.
[libpng17] Avoid a scan-build warning in pngtest.c