Fixed a minor bug: now the FCC mask for TV exclusions will automatically
choose to not apply wireless microphone exclusions (applying them does
not make sense in this case). This removes ambiguity and prevents
duplication of data.
Created a new helper function save_temp_filename(). Its function is
similar to that of save_filename() but it stores data in the temp
directory (as given by get_simulation_value('temp_dir')) instead of the
standard directories. This function is intended to be used for data
which can be discarded after the function has completed successfully.

Modified make_hex.m to make use of this new function.