(view-remove-frame-by-deleting): Change default value to t.

(view-remove-frame-by-deleting): Change default value to t.
Add autoload cookie.
(view-exit-action, view-file, view-file-other-window)
(view-file-other-frame, view-buffer, view-buffer-other-window)
(view-buffer-other-frame): Rewrite doc strings.
(view-return-to-alist-update): New function to remove stale entries
from view-return-to-alist.
(view-mode-enter): Rewrite doc string and simplify code.
(view-mode-exit): Handle new case 'keep-frame.  Don't reset
view-exit-action to nil.  Simplify code and rewrite doc string.