VC, read-only buffers for writable files

["Stefan Monnier" <monnier+gnu/emacs@rum.cs.yale.edu>]

It had been decided to postpone the decision to post-21.1,
so I think it's time to make a decision now.

Currently VC sometimes makes a file read-only because it thinks it's
better that way for the user.  More specifically, it makes it read-only
if the file seems to be locked by another user.

This can cause problems when VC gets the lock's ownership wrong
or when people are purposefully setting up access rights such
that anybody who's part of a particular group should be able to edit
the checked-out file.

It might be able to help the user avert a mistake in a few cases,
but that's only if the file's permissions are setup incorrectly.
If the file's permissions are not setup properly, then the user will
probably encounter many other risks anyway so what should happen in this
case is that the permissions should be fixed.

But Emacs has no way to tell whether the discrepency is because the
user has set things up in a slightly non-standard way, or whether it's
because Emacs is confused, or whether it's indeed because the file should
be read-only.

This special behavior used to apply to SCCS, RCS and CVS under Emacs-20
and was silently changed in Emacs-21 to only apply to RCS and SCCS (it was
changed as a side effect of another change).  Nobody complained about
this change and I think we should go further and remove this hack
altogether so it doesn't aply to RCS and SCCS either.


	Stefan