Report errors better with cal()

dotfiles/config/bashum/main.bashrc

         64:*)
             command cal -M "$@"
             ;;
+        127:*)
+            echo >&2 "cal(): cal command is not installed"
+            return 127
+            ;;
+        *)
+            echo >&2 "cal(): error: cal_es=$cal_es, cal_v=$cal_v"
+            return 5
+            ;;
     esac
 }