libpng: Squashed update to version 1.2.51

[legacy] Updated ANNOUNCE

[legacy] Bump version to libpng-1.2.47beta01

[legacy] Updated contrib/pngminus/makefile.std

[legacy] Reverted non-portable GNU syntax in makefile (?=, +=)

[legacy] Deleted some extra blank lines from visualc6 and 71 README files.

[libpng12] Imported from libpng-1.2.47rc01.tar

[libpng12] Imported from libpng-1.2.47.tar

[libpng12] Bump version to 1.2.48beta01

[libpng12] Removed two useless #ifdef directives from pngread.c and

one from pngrutil.c

[libpng12] Eliminated redundant png_push_read_tEXt|zTXt|iTXt|unknown code from

    pngpread.c and use the sequential png_handle_tEXt, etc., in pngrutil.c;
    now that png_ptr->buffer is inaccessible to applications, the special
    handling is no longer useful.

[libpng12] Fixed bug with png_handle_hIST with odd chunk length (Frank Busse).

[libpng12] Fixed off-by-one bug in png_handle_sCAL() when using fixed point

arithmetic, causing out-of-bounds read in png_set_sCAL() because of failure
to copy the string terminators (Franke Busse).

[libpng12] Imported from libpng-1.2.48beta01.tar

[libpng12] Bump version to 1.2.48beta02

[libpng12] Removed png_free() of unused png_ptr->current_text from pngread.c.

[libpng12] Added libpng license text to pnggccrd.c and pngvcrd.c

(requested by Chrome).

[libpng12] Imported from libpng-1.2.48rc02.tar

[libpng12] Update ANNOUNCE about pnggccrd.c change

[libpng12] Fixed date in ANNOUNCE.

[libpng12] Imported from libpng-1.2.48.tar

[libpng12] Update version numbers in ANNOUNCE

[libpng12] Imported from libpng-1.2.49.tar

[libpng12] Imported from libpng-1.2.50.tar

[libpng12] Ignore, with a warning, out-of-range value of num_trans

in png_set_tRNS().

[libpng12] Update copyright year in recently-changed files

[libpng12] Bump version to 1.2.51beta01

[libpng12] Changed AM_CONFIG_HEADER(config.h) to AC_CONFIG_HEADERS([config.h])

in configure.ac

[libpng12] Changed default value of PNG_USER_CACHE_MAX from 0 to 32767

in pngconf.h.

[libpng12] Imported from libpng-1.2.51beta01.tar

[libpng12] Bump version to 1.2.51beta02

[libpng12] Avoid a possible memory leak in contrib/gregbook/readpng.c

[libpng12] Update GIT URL in the manual.

[libpng12] Updated README description of contrib and projects directories

[libpng12] Imported from libpng-1.2.51beta02.tar

[libpng12] Bump version to 1.2.51beta03

[libpng12] Fix spelling of "doclifter" in CHANGES and ANNOUNCE

[libpng12] Changed '"%s"m' to '"%s" m' in png_debug macros to improve

portability among compilers.

[libpng12] Updated copyright year in recently-changed files.

[libpng12] Rebuilt configure scripts with autoconf-2.69 and automake-1.14.1

[libpng12] Updated copyright year in png.c.

[libpng12] Imported from libpng-1.2.51beta03.tar

[libpng12] Bump version to 1.2.51beta04

[libpng12] Removed potentially misleading warning from png_check_IHDR().

[libpng12] Imported from libpng-1.2.51beta04.tar

[libpng12] Bump version to 1.2.51beta05

[libpng12] Quiet set-but-not-used warnings in pngset.c

[libpng12] Imported from libpng-1.2.51beta05.tar

[libpng12] Imported from libpng-1.2.51rc01.tar

[libpng12] Quiet an uninitialized memory warning from VC2013 in png_get_png().

[libpng12] Imported from libpng-1.2.51rc02.tar

[libpng12] Quiet unused variable warnings from clang by porting PNG_UNUSED()

from libpng-1.4.6.

[libpng12] Imported from libpng-1.2.51rc03.tar

[libpng12] Removed a stray semicolon after PNG_UNUSED(params) in pngread.c

[libpng12] Update "last changed" info in source files.

[libpng12] Added "-D_SOLO" to contrib/pngminim makefiles (for zlib-1.2.6+)

[libpng12] Imported from libpng-1.2.51rc04.tar

[libpng12] Added an #ifdef PNG_FIXED_POINT_SUPPORTED/#endif in pngset.c

[libpng12] Imported from libpng-1.2.51.tar

Change-Id: Ia89e7d1e5c17a1c1b179d0b805ba5427d5d54ca2