message: Fix `make distcheck` by updating the icon cache on uninstall too
  Run gtk-update-icon-cache even on uninstall to clear the icon cache and
  avoid the following `make distcheck' error:
  ERROR: files left after uninstall:
  ./share/icons/hicolor/icon-theme.cache
  See
diff: @@ -50,5 +50,8 @@ dist_uiicons_DATA = \
  StatusWarningBlack.png \
  window-close.png
  -install-data-hook:
  +update-icon-cache:
  which gtk-update-icon-cache >/dev/null && gtk-update-icon-cache -f -t $(DESTDIR)$(iconsdir) || true
  +
  +install-data-hook: update-icon-cache
  +uninstall-hook: update-icon-cache
  