Replaced tabulators to 4 space characters in calc_model_free.py.
This corresponds to the removed_tab_in_modelfree_patch file attached to https://gna.org/task/?6847
by Michael Bieri (https://gna.org/users/michaelbieri), in the zip file
https://gna.org/support/download.php?file_id=7726.
This patch contained far more changes than just the tab fixes, but only that part is being committed
here. The gui_bieri.relax_gui changes appear to be in the other patches anyway.
