Add build rule for build-octave (bug #49503). * src/build-octave.mk: Add new build rule for build-octave which can be used for cross-building binary packages that depend on Octave as a build tool. * dist-files.mk: Add new file to list. * index.html: Add new package to list. * src/of-communications.mk, src/of-image.mk, src/of-mapping.mk, src/of-optiminterp.mk, src/of-sparsersb.mk, src/of-statistics.mk, src/of-windows.mk: Add optional dependency on build-octave. * configure.ac: Add new configure switch "--disable-system-octave" that is needed to build the build-octave package. * Makefile.in: Add variable "USE_SYSTEM_OCTAVE". Exclude build-octave from the default build tools and build it only if a package explicitly depends on it. Display warning about missing native Octave version only if necessary.

#!/usr/bin/env bash
set -eu

if [ "$#" -ne 2 ]; then
    echo
    echo "Syntax: $0 [IMAGE.png] [NAME]"
    echo
    echo 'IMAGE.png -> screenshot-NAME.png + screenshot-NAME-small.png'
    echo
    exit 1
fi

set -v

IMAGE_FILE="$1"
NAME="$2"

cat "$IMAGE_FILE" \
| pngtopnm \
| pnmtopng -compression 9 \
> "screenshot-$NAME.png"

cat "screenshot-$NAME.png" \
| pngtopnm \
| pnmscale -ysize 128 \
> "screenshot-$NAME-small.pnm"

pnmquant 256 "screenshot-$NAME-small.pnm" \
| pnmtopng -compression 9 \
> "screenshot-$NAME-small.png"

rm -f "screenshot-$NAME-small.pnm"