cvsclient: Do not abort checkout when skipping $Log$ keyword expansion

Some CVS servers have restriction regarding the expansion of the

$Log$

keyword in file to checkout and might skip that operation (see doc).

Nevertheless, official CVS client will still checkout the file but without expanding the

$Log$

keyword so we should have the same behavior in the loader.

$ export CVSROOT="anoncvs@anoncvs.NetBSD.org:/cvsroot"
$ export CVS_RSH="ssh"
$ cvs checkout -r 1.1.1.1 src/usr.bin/rcs/doc/rcs.ms
cvs checkout: Skipping `$Log$' keyword due to excessive comment leader.
U src/usr.bin/rcs/doc/rcs.ms

Closes #4646 (closed)

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Migrated from D8750 (view on Phabricator)