instead of memset to zero in png_read_png().

They were only useful for obtaining compatibility for old applications
that used libpng-1.0.x versions prior to the implementation of "free_me".

It does not seem to promise any benefit to libpng.

To try this, configure libpng using PNG_USE_MEMSET_LOOP.  Initial testing
with pngcrush was not promising, although it does save a hundred bytes or
so of executable size.

1. Modify project(PNG) to project(PNG C) to avoid search for C++ compiler
2. set(CMAKE_ALLOW_LOOSE_LOOP_CONSTRUCTS true) and fix end conditionals
from ugly else(FOO AND BAR) endif(FOO AND BAR) to else() endif()
3. Add missing include_directories() for ZLIB_INCLUDE_DIR
4. Created CMake options to allow configurable building of STATIC or SHARED
libpng, both default on.
5. Modified PNG_DEBUG to default to false?
6. Fix installation of static/shared libraries so DLL goes in prefix+/bin,
all others in prefix+/lib

lpXYZ.tar.bz2 (with CRLF), KNOWNBUG, libpng-x.y.z-KNOWNBUG.txt,
and the "noconfig" files have been removed from the distribution.

It had been put inside the png_debug2() statement.

PNG_UNKNOWN_CHUNK_SUPPORTED should be PNG_HANDLE_AS_UNKNOWN_SUPPORTED.

in pngwutil.c, that was recently added by mistake.

with information that the NULL dereference bug first appeared in libpng-0.95.

in png_set_text-2().  Bug discovered by Evan Rouault, using cochinelle.

in png.c (suggested by Peter Breitenlohner)

from the new call to png_read_gray_to_rgb() (bug introduced in
libpng-1.4.0beta67). (Patch contributed by Alam Arias)

The AVG and PAETH filters will never be selected for the first
row, so we need not test them.

and png_write_png().