[libpng16] Removed #error macro from contrib/tools/pngfix.c (Thomas Klausner).
[libpng16] Merged pngrio.c, pngtrans.c, pngwio.c, and pngerror.c

with libpng-1.7.0
[libpng16] Merged libpng-1.7.0 changes to make no-interlace configurations work

with test programs.
[libpng16] Revised pngvalid.c to support libpng 1.5, which does not support the

PNG_MAXIMUM_INFLATE_WINDOW option, so #define it out when appropriate in
pngvalid.c
Allow unversioned links created on install to be disabled in configure In configure builds 'make install' changes/adds links like png.h and libpng.a to point to the newly installed, versioned, files (e.g. libpng17/png.h and libpng17.a). Three new configure options and some rearrangement of Makefile.am allow creation of these links to be disabled.

Signed-off-by: John Bowler <jbowler@acm.org>