[libpng16] tests backported from libpng 1.7

This updates libpng16 with all the test changes from libpng17,
including changes to pngvalid.c to ensure that the original,
distributed, version of contrib/visupng/cexcept.h can be used.

pngvalid contains the correction to the use of SAVE/STORE_
UNKNOWN_CHUNKS; a bug revealed by changes in libpng 1.7.  More
tests contain the --strict option to detect warnings and the
pngvalid-standard test has been corrected so that it does not
turn on progresive-read (there is a separate test which does
that.)

Some signed/unsigned fixes have been made.

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

tests/pngimage-full

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngimage --exhaustive --log "${srcdir}/contrib/pngsuite/"*.png
+exec ./pngimage --exhaustive --list-combos --log "${srcdir}/contrib/pngsuite/"*.png

tests/pngimage-quick

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngimage --log "${srcdir}/contrib/pngsuite/"*.png
+exec ./pngimage --list-combos --log "${srcdir}/contrib/pngsuite/"*.png

tests/pngunknown-IDAT

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngunknown default=discard IDAT=save "${srcdir}/pngtest.png"
+exec ./pngunknown --strict default=discard IDAT=save "${srcdir}/pngtest.png"

tests/pngunknown-discard

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngunknown default=discard "${srcdir}/pngtest.png"
+exec ./pngunknown --strict default=discard "${srcdir}/pngtest.png"

tests/pngunknown-if-safe

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngunknown default=if-safe "${srcdir}/pngtest.png"
+exec ./pngunknown --strict default=if-safe "${srcdir}/pngtest.png"

tests/pngunknown-sAPI

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngunknown bKGD=save cHRM=save gAMA=save all=discard iCCP=save sBIT=save sRGB=save "${srcdir}/pngtest.png"
+exec ./pngunknown --strict bKGD=save cHRM=save gAMA=save all=discard iCCP=save sBIT=save sRGB=save "${srcdir}/pngtest.png"

tests/pngunknown-sTER

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngunknown sTER=if-safe "${srcdir}/pngtest.png"
+exec ./pngunknown --strict sTER=if-safe "${srcdir}/pngtest.png"

tests/pngunknown-save

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngunknown default=save "${srcdir}/pngtest.png"
+exec ./pngunknown --strict default=save "${srcdir}/pngtest.png"

tests/pngunknown-vpAg

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngunknown vpAg=if-safe "${srcdir}/pngtest.png"
+exec ./pngunknown --strict vpAg=if-safe "${srcdir}/pngtest.png"

tests/pngvalid-standard

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngvalid --standard --progressive-read
+exec ./pngvalid --standard