packaging: always execute builddeb from source root

Without this, dockerdeb and the make targets that invoke it may
fail depending on the pwd at the time of invocation.

contrib/packaging/dockerdeb

@@ -1,40 +1,40
 #!/bin/bash -eu
 
 . $(dirname $0)/packagelib.sh
 
 BUILDDIR=$(dirname $0)
 export ROOTDIR=$(cd $BUILDDIR/../.. > /dev/null; pwd)
 
 DISTID="$1"
 CODENAME="$2"
 PLATFORM="$1-$2"
 shift; shift # extra params are passed to build process
 
 OUTPUTDIR=${OUTPUTDIR:=$ROOTDIR/packages/$PLATFORM}
 CONTAINER=hg-docker-$PLATFORM
 
 DOCKER=$($BUILDDIR/hg-docker docker-path)
 
 $BUILDDIR/hg-docker build \
     --build-arg CODENAME=$CODENAME \
     $BUILDDIR/docker/$DISTID.template \
     $CONTAINER
 
 # debuild only appears to be able to save built debs etc to .., so we
 # have to share the .. of the current directory with the docker
 # container and hope it's writable. Whee.
 dn=$(basename $ROOTDIR)
 
 DBUILDUSER=build
 
 if [ $(uname) = "Darwin" ] ; then
     $DOCKER run -u $DBUILDUSER --rm -v $PWD/..:/mnt $CONTAINER \
             sh -c "cd /mnt/$dn && make clean && make local"
 fi
 $DOCKER run -u $DBUILDUSER --rm -v $ROOTDIR/..:/mnt $CONTAINER \
   sh -c "cd /mnt/$dn && DEB_BUILD_OPTIONS='${DEB_BUILD_OPTIONS:=}' contrib/packaging/builddeb --build --distid $DISTID --codename $CODENAME $@"
-contrib/packaging/builddeb --cleanup --distid $DISTID --codename $CODENAME
+(cd $ROOTDIR && contrib/packaging/builddeb --cleanup --distid $DISTID --codename $CODENAME)
 if [ $(uname) = "Darwin" ] ; then
     $DOCKER run -u $DBUILDUSER --rm -v $PWD/..:/mnt $CONTAINER \
             sh -c "cd /mnt/$dn && make clean"
 fi