This reverts commit 97dfccb6.

pngwrite.c, pngunknown.c, and pngvalid.c.  Several warnings still remain
in pngvalid.c

Remove all currently detected cases of unsigned overflow.  Detection is
runtime, so test case dependent.  The changes to pngvalid.c eliminate
spurious and probably invalid tests with one while loop exception.

Apart from that and the change to the dependence on the intended
unsigned overflow in pngtrans.c the changes are limited to altering the
meme for an unsigned 'x' from:

   while (x-- > 0)

to

   for (; x > 0; --x)

This works because, in all cases, the control variable is not used in
the loop.  The 'while' meme was, at one time, warn'ed by GCC so it is
probably a good change, for some weird religious value of good.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

flag definitions in pngpriv.h from 0xnnnn to 0xnnnnU and trivial changes
in png.c, pngread.c, and pngwutil.c.

flag definitions in pngpriv.h from 0xnnnn to 0xnnnnU.

Merged pngtest.c with libpng-1.7.0beta84/pngtest.c

ignore the ADLER32 checksum in the IDAT chunk as well as the chunk CRCs.

and pngrutil.c.

while decoding compressed data chunks.

Because png_handle_pCAL has allocated memory to free.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

When an input file contains a zero length IDAT and pngfix is not applying the
IDAT rechunking (--max) option pngfix will go into a loop writing the zero
length IDAT for ever.

This is a fairly minor issue for interactive use; zero length IDAT is very rare,
the problem is obvious (pngfix hangs) and the fix (use --max, or --max=4096
etc), while not obvious, is easy.

For non-interactive use, e.g. trying to automatically repair a PNG that cannot
be read by libpng, there are security consequences:

1) pngfix hangs.  This may permit a DoS attack.
2) When the --out option is used pngfix will just keep writing.  This is a very
likely DoS scenario.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

    1. png_read_filter_row_sub4_msa
    2. png_read_filter_row_avg4_msa
    3. png_read_filter_row_paeth4_msa
    4. png_read_filter_row_sub3_msa
    5. png_read_filter_row_avg3_msa
    6. png_read_filter_row_paeth3_msa
Signed-off-by: NMandar Sahastrabuddhe <Mandar.Sahastrabuddhe@imgtec.com>

Update from original

Also added one msa optimized function: png_read_filter_row_up_msa
Signed-off-by: NMandar Sahastrabuddhe <Mandar.Sahastrabuddhe@imgtec.com>