Update: rewrite fll_execute, ensuring f_eol are properly added (and auto-add progam...

Update: rewrite fll_execute, ensuring f_eol are properly added (and auto-add progam name where possible)

Previously, the f_eol was added but it assumed that there was actual room at the end of the allocated buffer to do so.
This now explicilty allocates a new buffer with room for the terminating f_eol.

The progam name is already provided, so do not require it to be added to the arguments (auto-add it).