initial implementation of stagedata-in-repodata

[classabbyamp]

sorry in advance for my poor go

tested with:

export XBPS_ARCH=x86_64 XBPS_TARGET_ARCH=x86_64
mkdir -p /tmp/test-repo /tmp/test-repo2 /tmp/pkg
xbps-create -A noarch -n foo-1.0_1 -s "foo pkg" --shlib-provides='libfoo.so.1' /tmp/pkg
cp foo-1.0_1.noarch.xbps /tmp/test-repo
cp foo-1.0_1.noarch.xbps /tmp/test-repo2
xbps-create -A noarch -n bar-1.0_1 -s "bar pkg" --shlib-requires='libfoo.so.1' /tmp/pkg
cp bar-1.0_1.noarch.xbps /tmp/test-repo
cp bar-1.0_1.noarch.xbps /tmp/test-repo
xbps-rindex -a /tmp/test-repo/*.xbps
xbps-rindex -a /tmp/test-repo2/*.xbps
# force staging in test-repo
xbps-create -A noarch -n foo-2.0_1 -s "foo pkg" --shlib-provides='libfoo.so.2' /tmp/pkg
cp foo-2.0_1.noarch.xbps /tmp/test-repo
xbps-rindex -a /tmp/test-repo/*.xbps

used in void-linux/repo-exporter#4