(calc-mode-map): Add keybinding for `calc-transpose-lines'.

lisp/calc/calc.el

@@ -1022,6 +1022,7 @@ Used by `calc-user-invocation'.")
     (define-key map "\"" 'calc-auto-algebraic-entry)
     (define-key map "\t" 'calc-roll-down)
     (define-key map "\M-\t" 'calc-roll-up)
+    (define-key map "\C-x\C-t" 'calc-transpose-lines)
     (define-key map "\C-m" 'calc-enter)
     (define-key map "\M-\C-m" 'calc-last-args-stub)
     (define-key map "\C-j" 'calc-over)