cvs-add-secondary-branch-prefix is a compiled Lisp function in `
(cvs-add-secondary-branch-prefix FLAGS &optional ARG)
Add branch selection argument if the secondary branch prefix was set.
The argument is added (or not) to the list of FLAGS and is constructed
by appending the branch to ARG which defaults to "-r".
Since the `cvs-secondary-branch-prefix' is only active if the primary
prefix is active, it is important to read the secondary prefix before
the primary since reading the primary can deactivate it.