smithlab_cpp not allowed to be an external copy?

[andrewdavidsmith]

How come there is no allowance for people who already have a SMITHLAB_CPP variable defined? Must everyone use a fresh copy hardcoded into zagros?

[pjuren]

What is the advantage of allowing people to change it? We know the commit that is checked out with Zagros when the repos is cloned works with our code. Some other version might not.