[libpng17] Fixed makepng.c so that it compiles with GCC 5.1.0.

Added contrib/testspngs/: a directory for additional test png files

contrib/testpngs/makepngs.sh

@@ -0,0 +1,72 @@
+#!/bin/sh
+#
+# Make a set of test PNG files, MAKEPNG is the name of the makepng executable
+# built from contrib/libtests/makepng.c
+#
+# The arguments say whether to build all the files or whether just to build the
+# ones that extend the code-coverage of libpng from the existing test files in
+# contrib/pngsuite.
+test -n "$MAKEPNG" || MAKEPNG=./makepng
+
+mp(){
+   ${MAKEPNG} $1 "$3" "$4" "$2$3-$4.png"
+}
+
+mpg(){
+   if test "$g" = "none"
+   then
+      mp "" "" "$2" "$3"
+   else
+      mp "--$1" "$1-" "$2" "$3"
+   fi
+}
+
+case "$1" in
+   --all)
+      for g in none sRGB linear 1.8
+      do
+         for c in gray palette
+         do
+            for b in 1 2 4
+            do
+               mpg "$g" "$c" "$b"
+            done
+         done
+
+         mpg "$g" palette 8
+
+         for c in gray gray-alpha rgb rgb-alpha
+         do
+            for b in 8 16
+            do
+               mpg "$g" "$c" "$b"
+            done
+         done
+      done;;
+
+   --coverage)
+      # Comments below indicate cases known to be required and not duplicated
+      # in other (required) cases; the aim is to get a minimal set that gives
+      # the maxium code coverage.
+      mpg none gray 16
+      mpg none gray-alpha 16
+      mpg none gray-alpha 8 # required
+      mpg none palette 8
+      mpg none rgb-alpha 8
+      mpg 1.8 gray 2
+      mpg 1.8 palette 2 # required
+      mpg 1.8 palette 4 # required
+      mpg 1.8 palette 8
+      mpg linear palette 8
+      mpg linear rgb-alpha 16
+      mpg sRGB gray-alpha 8
+      mpg sRGB palette 1 # required
+      mpg sRGB palette 8
+      mpg sRGB rgb-alpha 16 # required pngread.c:2422 untested
+      mpg sRGB rgb-alpha 8;;
+
+   *)
+      echo "$0 $1: unknown argument, usage:" >&2
+      echo "  $0 [--all|--coverage" >&2
+      exit 1
+esac