(line-move-visual): Make it a defcustom.

(line-move-visual): Make it a defcustom.
(line-move-1): Convert temporary-goal-column back to an integer if
it was set as a float by a previous call to line-move-visual.
(end-of-visual-line, beginning-of-visual-line, kill-visual-line)
(next-logical-line, previous-logical-line)
(turn-on-visual-line-mode): New functions.
(visual-line-mode-map): New variable.
(visual-line-mode, global-visual-line-mode): New minor mode.