(flyspell-auto-correct-binding, flyspell-incorrect-face)

(flyspell-auto-correct-binding, flyspell-incorrect-face)
(flyspell-duplicate-face): Use (X)Emacs-agnostic code.
(flyspell-mode-map): Don't overwrite at each load.  Remove code
redundant with the subsequent add-minor-mode.  Merge Emacs and XEmacs code.
(flyspell-word): Minor simplification.
(flyspell-math-tex-command-p): Quieten the byte-compiler.
(flyspell-external-point-words): Remove unused vars `size' and `start'.
(flyspell-do-correct): Rename from flyspell-xemacs-correct.
Merge the corresponding Emacs code.
(flyspell-correct-word, flyspell-xemacs-popup): Use flyspell-do-correct.