[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