Fix computation of objective function in OSR if covariances are specified

Due to the preprocessor adding entries for all variable combination into i_var, variables contained in covariances obtained a wrong weighting. By only selecting the unique entries, this cannot happen anymore. Moreover, the computation intensity of the objective does not increase quadratically in the objective anymore.
Add unit test to check whether objective function matches and whether covariances actually work
Transform objective function in osr to full matrix

If the objective function only has one element, the scalar product of a sparse matrix and a full matrix is sparse (in contrast to two or more elements). This crashes the osr code subsequently.
Fix bug in osr where moments were not based on optimal parameter draw

M_.params is global and was set by csminwel1 to the last value tested; this does not necessarily coincide with the optimal parameter vector, which may have occurred earlier. This commit explicitly sets the optimal parameter vector.
Computation of the loss function in the presence of unit root variables was incorrect

Some elements were simply left out. This commit now mimics the computations as in th_autocovariances.m and makes sure the loss function coincides with the one that is obtained by reading out the covariance from oo_.var
Add unit test for correct computation of loss function in the presence of non-stationary variables
Merge pull request #767 from JohannesPfeifer/osr_scaling

Fix computation of objective function in OSR when covariances are specified