## Clear up option mh_posterior_mode_estimation

See the question at http://www.dynare.org/phpBB3/viewtopic.php?f=1&t=7235
Does anyone know what it does?
Looking at the codes in `dynare_estimation_1.m`

this option seems to skip mode computation and directly runs the MCMC, using the prior mode as the starting point and the prior variances for computing the inverse Hessian for the MCMC. In case of the mode not existing, the prior mean is used.
But already before doing so, it sets

```
oo_.posterior.optimization.mode = xparam1;
oo_.posterior.optimization.Variance = [];
```

That is, the mode saved is based on the starting values given for MCMC and no variance is saved. This looks like a a bug as the MCMC starts with values that are only set after this assignment.

Finally, this option runs the MCMC and calls `CutSample.m`

before returning. What is the point of just estimating the MCMC starting at the prior mode and providing no output?

We should either document the option and add a preprocessor command or get rid of it.