Check the usage of virtualenv(s) before the uninstallation of versions

etc/pyenv.d/uninstall/virtualenv.bash

@@ -0,0 +1,25 @@
+VERSION_NAME="${DEFINITION##*/}"
+PREFIX="${PYENV_ROOT}/versions/${VERSION_NAME}"
+
+if ! pyenv-virtualenv-prefix "${VERSION_NAME}" 1>/dev/null 2>&1; then
+  OLDIFS="$IFS"
+  IFS=$'\n' virtualenvs=($(pyenv-virtualenvs --bare))
+  IFS="$OLDIFS"
+
+  declare -a dependencies
+  for venv in "${virtualenvs[@]}"; do
+    venv_prefix="$(pyenv-virtualenv-prefix "${venv}" 2>/dev/null || true)"
+    if [ -d "${venv_prefix}" ] && [ "${PREFIX}" = "${venv_prefix}" ]; then
+      dependencies[${#dependencies[*]}]="${venv}"
+    fi
+  done
+
+  if [ -z "$FORCE" ] && [ -n "$dependencies" ]; then
+    echo "pyenv: ${#dependencies[@]} virtualenv(s) is depending on $PREFIX." >&2
+    read -p "continue with uninstallation? (y/N) "
+    case "$REPLY" in
+    y* | Y* ) ;;
+    * ) exit 1 ;;
+    esac
+  fi
+fi