clarified: a variant of -i is the default, but its output is not as precise as it might seem;
#!/usr/bin/env bash
#
# Author: Florian Haftmann, TU Muenchen
#
# DESCRIPTION: pie chart with Mercurial churn statistics
ALIAS="${1:-$ISABELLE_HOME/Admin/user-aliases}"
shift
SCRIPT="$ISABELLE_HOME/Admin/lib/scripts/churn_pie"
cd "$(dirname "$ALIAS")"
hg churn --aliases "$ALIAS" | "$SCRIPT" "$@"