force console mode when matlab started with -nojvm or -nodisplay flags or octave started with --no-window-system flag (ticket 283)

data by error if available data are shorter than declared sample

Added the possibility to write graph_format=none, in which case the graphs are displayed (provided nograph and nodisplay options are not used) but not saved.

labels in Policy and Transition Functions.

can't be used for data, but it happens that dates for example don't
have a column headings

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.