computes the exact mu_j in both the standard form and nonstandard form case
- fixed bug in ratio_test_1__t_j() where mu_j was not correctly computed for
problems in nonstandard form
slack variable
- fixed bug in which the partial pricing called mu_j(j) for a variable j which
is basic (the reason is that the active set MAY contain basic variables;
these were priced in previous revisions)