cvs-plugin doesn't catch file changes if the files are checked out with -f -r (HEAD or branch)

When checking out a cvs repository with Branch and Use HEAD revision if tag not found, the Changes list is always empty even though the build was triggered by scm changes that are picked up the by cvs update in the build log.

Since the use Head function was introduced by me in 1.5, maybe the update check is broken in a way I didn't notice, I will try to fix this.