(calc-do-keypad): Don't attempt to use nonexistent global
mouse-map, use calc-keypad-map.
(calc-keypad-x-left-click): Renamed to calc-keypad-left-click.
(calc-keypad-left-click): Don't use mouse-map; update to new event
interface.
(calc-keypad-x-middle-click, calc-keypad-x-right-click): Ditto.
(calc-keypad-press): Use `unread-command-events' instead of
`unread-command-char'.
(calc-minibuffer-size): New.
(calcDigit-nondigit): Use it instead of `buffer-size'.
(calcDigit-backspace): Likewise.
(calcDigit-nondigit): Use `minibuffer-contents' instead of `buffer-string'.
(calc-minibuffer-contains): Use `minibuffer-prompt-end' instead of `point-min'.
(calcDigit-key): Use `calc-minibuffer-contains' instead of a `save-excursion'.
(calc-do-quick-calc): Use `frame-width' instead of `screen-width'.
(calcAlg-edit): Use `minibuffer-contents' instead of `buffer-string'.
(calcAlg-enter): Likewise.
(calcAlg-enter): Use `minibuffer-prompt-end' instead of `point-min'.
