The commit removes the three compile warning options from the individual project
files into the zlib.props globals (this should probably be renamed in 1.7).  It
increases the warning level from 4 to All and adds a list of the warnings which
need to be turned off.  This is semi-documentary; the intent is to tell users of
libpng which warnings have been examined and judged non-fixable at present.

The warning about structure padding *IS* fixable, but it is a signficant change
(moving structure members around).  It is currently partially fixed in 1.7, but
only partially.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

The SKIP definition needs to come after the png.h include (see all the other .c
files in contrib/libtests) because it depends on PNG_LIBPNG_VER.  This commit
puts it in the correct place.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

MSVC does not like (uInt) = -(unsigned) (i.e. as an initializer), but it is fine
with it if the conversion is explicitly invoked by a cast.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

MSVC doesn't like '-(unsigned)', so replace it by 0U-(unsigned) (in 1.6).
Signed-off-by: NJohn Bowler <jbowler@acm.org>

only one filter is a candidate for selection. This trades off code size (added
png_setup_*_row_only() functions) for speed.

is not used within libpng, but is used in some of the examples.

This covers the case where PNG_IMAGE_BUFFER_SIZE can overflow in the application
as a result of the application using an increased 'row_stride'; previously
png_image_finish_read only checked for overflow on the base calculation of
components.  (I.e. it checked for overflow of a 32-bit number on the total
number of pixel components in the output format, not the possibly padded row
length and not the number of bytes, which for linear formats is twice the number
of components.)
Signed-off-by: NJohn Bowler <jbowler@acm.org>

memcpy() with a null source, even if count is zero (Leon Scroggins III).

Coverity rejects code where an array element count has type size_t, this
elminates the code in question from contrib/libtests/pngvalid.c
Signed-off-by: NJohn Bowler <jbowler@acm.org>

The previous version of the code invariably passed just one byte at a time to
libpng.  The intention was to pass a random number of bytes in the range 0..511
(and this is what happens now).
Signed-off-by: NJohn Bowler <jbowler@acm.org>

positions.  Fixed the sequential reader to handle these more robustly
(John Bowler).

properly (patch by Timothy Nikkel).