magic code in initAndValidate

[tgvaughan]

The initAndValidate() for the CalibratedYuleModel class contains this code:

        if (nCals == 0) {
            // assume we are in beauti, back off for now
            return;
        }

Is this really the best BEAST2 can do for developers. How can a developer know if this magic is needed, and where? if there is no alternative, this must be very prominently and thoroughly documented.

[rbouckaert]

Merge with issue #25

[rbouckaert]

Close since this is duplicate of #25