User model choice being ignored in bruvo.msn

[zkamvar]

Current workaround solution: calculate bruvo's distance with bruvo.dist() and then feed it into poppr.msn()

Problem: all calls to bruvo.dist() from bruvo.msn() and poppr:::singlepop_msn() do not give the add or loss parameters, thus defaulting to average over genome loss and genome addition models, despite the user choice.

I will fix these in poppr's current devel branch and then make a pull request for @JonahBrooks so that he can incorporate it into his code.