Option variable
file_output_appendDefault value: false
file_output_append governs whether file output functions
append or truncate their output file.
When file_output_append is true,
such functions append to their output file.
Otherwise, the output file is truncated.
save, stringout, and with_stdout respect file_output_append.
Other functions which write output files do not respect file_output_append.
In particular, plotting and translation functions always truncate their output file,
and tex and appendfile always append.