Filter out use of loglinear with simulated moments

Does not work because steady state is not logged
Fix option loglinear for stoch_simul.m by also logging steady state.

Must be done to assure correct simulations and output of moments. Cannot be done in the solver itself as estimation performs logging of steady state also outside of solver
Clarify the role of the loglinear option for stoch_simul
Make sure repeated runs of stoch_simul.m with loglinear option do not crash due to logged steady state
Add unit test for loglinear option
Make sure that estimation works after loglinear option in stoch_simul with initval-block

stoch_simul logs the steady state. Here, it is transformed back
Get rid of redundant initval in fs2000.mod

Was replaced by steady_state-model-block
More explicit commenting of stoch_simul.m related to loglinear option
Added a routine to test if we are currently estimating a model.
Cosmetic changes.
Check if the steady state is strictly positive when simulating/estimating a model with loglinear option.
Merge branch 'loglinear'