[libpng16] Check for __has_extension before using it in pngconf.h, to

support older Clang versions (Jeremy Sequoia).
[libpng16] Use a user warning handler in contrib/gregbook/readpng2.c

instead of the default.
[libpng16] Added png_ptr->process_mode = PNG_READ_IDAT_MODE in

png_push_read_chunk after recognizing the IDAT chunk, which avoids an
infinite loop while reading a datastream whose first IDAT chunk is of
zero-length.
[libpng16] Don't recognize known sRGB profiles as sRGB if they have been hacked.
[libpng16] Don't recognize known sRGB profiles as sRGB if they have been hacked,

but don't reject them and don't issue a copyright violation warning.
Simplified code in pngrutil.c that decides whether to warn about an
incorrect ancillary PLTE chunk.
[libpng16] Imported from libpng-1.6.10beta02.tar
[libpng16] Bump version to 1.6.10beta03
[libpng16] Fixed some nits in contrib/arm-neon/README and comments in

contrib/examples/*.c
[libpng16] Document how to use a different crc_action while reading chunks

after IDAT with the sequential reader.
[libpng16] Moved some documentation from png.h to libpng.3 and libpng-manual.txt

and minor editing of contrib/arm-neon/README and contrib/examples/*.c
[libpng16] Removed some commentary from png.h that is now in the manual.
[libpng16] Imported from libpng-1.6.10beta03.tar
[libpng16] Bump version to 1.6.10beta04
[libpng16] Mention CERT VU#684412 and CVE-2014-0333 in CHANGES and ANNOUNCE.
[libpng16] Fixed typos in the manual and in scripts/pnglibconf.dfa (CFLAGS

-> CPPFLAGS and PNG_USR_CONFIG -> PNG_USER_CONFIG).
[libpng16] Imported from libpng-1.6.10rc01.tar
[libpng16] Bump version to 1.6.10rc01
[libpng16] Removed unreachable return statement after png_chunk_error()

in pngrutil.c
[libpng16] Imported from libpng-1.6.10rc02.tar
[libpng16] Updated CHANGES and ANNOUNCE to libpng-1.6.10rc02.