This is necessary to ensure that Octave Forge packages are loaded.

Closes: #222

- fix support for filenames with extension (.m, .mat, .xls), since the manual
  and the bison grammar both support it
- fix support for XLS files under Octave
- add support for XLSX files
- run test for loading XLS files

there is no metropolis history file

added tests for mode_compute=4 and mode_compute=6. They increase computing time of the
test suite by about 30 minutes.

Bug fix: graphic options are not passed to global options_ (for the next release try to skip the use of the global here).

This reverts commit fcceec89.

Save the names of the estimated parameters in <MODEL_NAME>_mode.mat when mode_compute is equal to six (stochastic optimization).

This should fix some random crashes of the preprocessor

ms-sbvar: remove unused field removal statements (and set options_.datafile='' in global_initialization)

Added an option to decide if dsge_likelihood should call univariate filters when the covariance matrix of
the prediction error is singular (default is yes).