Ensure all helper scripts pushd/popd

Make sure all of these move to the root of the repository first, then
return to where they were afterwards, using pushd/popd. This allows them
to be executed from anywhere in the repo.

build-deb.sh

@@ -1,4 +1,5 @@
 #!/bin/sh
+pushd $( git rev-parse --show-toplevel ) &>/dev/null
 ver="$( head -1 debian/changelog | awk -F'[()-]' '{ print $2 }' )"
 git pull
 rm ../pvc_*
@@ -6,3 +7,4 @@ find . -name "__pycache__" -exec rm -r {} \;
 dh_make -p pvc_${ver} --createorig --single --yes
 dpkg-buildpackage -us -uc
 dh_clean
+popd &>/dev/null