+# No local modifications allowed.
+case $(git diff-index --name-only HEAD) in
+ '') ;;
+ *) die 'this tree is dirty; commit your changes first';;
+esac
+
+# Ensure the current branch name is correct:
+curr_br=$(git rev-parse --symbolic-full-name HEAD)
+test "$curr_br" = refs/heads/$branch || die not on branch $branch
+