mergetools / ecmergeon commit symbolic-ref -d: do not allow removal of HEAD (12cfa79)
   1diff_cmd () {
   2        "$merge_tool_path" --default --mode=diff2 "$LOCAL" "$REMOTE"
   3}
   4
   5merge_cmd () {
   6        touch "$BACKUP"
   7        if $base_present
   8        then
   9                "$merge_tool_path" "$BASE" "$LOCAL" "$REMOTE" \
  10                        --default --mode=merge3 --to="$MERGED"
  11        else
  12                "$merge_tool_path" "$LOCAL" "$REMOTE" \
  13                        --default --mode=merge2 --to="$MERGED"
  14        fi
  15        check_unchanged
  16}