preprocessor

v4.1: Added Model comparison. Not yet ready but can be used. The preprocessor, surprisingly, seems to sort the compared models (listed after the model_comparison command) by decreasing order of the model names (including path and extension). 

TODO: 
+ Add an option to define the benchmark model (bayes ratio).
+ Add comparison to estimated BVAR models.

git-svn-id: https://www.dynare.org/svn/dynare/dynare_v4@2110 ac1d8469-bf42-47a9-8791-bf33cf982152