Tramp advises vc-workfile-unchanged-p, how to remove?

[Kai Großjohann]

I've taken a look at the advice of vc-workfile-unchanged-p.  It seems
to me that it was originally introduced because VC looked at the
modification timestamps of the files involed.  Did VC do that in
earlier releases, Andre?

Now, it seems that the workfile-unchanged-p operation is implemented
by invoking diff.  The default implementation should thus work more or
less out of the box for Tramp, as well.

The only exception to this is the RCS implementation.  It queries the
underlying RCS installation whether it groks "--brief".  Invoking RCS
remotely may refer to different RCS installations, so that we have to
remember different values for the "groks --brief" flag.

My suggestion is to augment tramp-vc-setup-for-remote to make
vc-rcsdiff-knows-brief a buffer-local variable.  This was already done
for vc-rcs-release.

What do people think?  Could this work?

Kai