Changes in XMBF 1.81:
---------------------

Fixed a bug in the calculation of derivatives of the model functions with respect to the "oo" amplitude parameters in the following models:

   threept_multi_alt_exp_model
   threept_multi_alt_exp_expE_model
   threept_multi_alt_exp_vec_model
   threept_multi_alt_exp_expE_vec_model

Detailed description of change: line 242 of "threept_multi_alt_exp_model.cpp" and "threept_multi_alt_exp_expE_model.cpp"
has been corrected from previously

    return alt(t)*alt(T-t)*eo_model->eval_derivative(function, mexp_final+mexp_initial+parameter, arguments);

to

    return alt(t)*alt(T-t)*oo_model->eval_derivative(function, mexp_final+mexp_initial+parameter, arguments);