(find-file, find-file-other-window,
find-file-read-only, find-file-read-only-other-window,
find-file-read-only-other-frame, find-alternate-file-other-window,
find-alternate-file): With a prefix argument, enable users to
specify a coding system interactively.
(find-file-noselect): Describe optional arguments NOWARN and
RAWFILE in the doc-string.
(write-file, insert-file, append-to-file): Accept a prefix
argument to enable users to specify a coding system interactively.
(revert-buffer): Read an auto-saved file without any code
conversion.