(message-fix-before-sending): Expose all invisible text with the property

(message-fix-before-sending): Expose all invisible text with the property
`message-invisible';
don't expose invisible X-Face fields;
widen at first.
(message-invisible-region): New function, substitute for `invisible-region'.
(message-send): Call `message-fix-before-sending' after evaluating
`message-send-hook'.
(message-check-ignore-invisible-x-face-field): Remove.  You can use
(add-hook 'message-send-hook 'x-face-xmas-remove-x-face-glyph) instead.