bug#50431: revert-buffer doesn't preserve read-onlyness

[Drew Adams]

> "Reverting" has a specific meaning: re-read the file from disk as if
> it were visited anew.  If the user wants to make additional
> adjustments, they will need to readjust.  I don't see why the
> read-only status should be exempt from this logic.

+1.
___

Consider Dired, which, by visiting a directory
is somewhat like visiting a file.  Dired's `g'
reverts the buffer, but that doesn't revert
all of the Dired state (markings, sort order,
hidden files, etc.).  `C-x C-v', on the other
hand, does "restore" to both revisit the file
system and restore Dired default (user) settings.

Both `g' and `C-x C-v' are useful in Dired.
Which is just another way of saying that there
can be multiple ways/kinds of "reverting".